diff --git a/cmd/sklad/container.tmpl b/cmd/sklad/container.tmpl
index 4bacae8..5bb5123 100644
--- a/cmd/sklad/container.tmpl
+++ b/cmd/sklad/container.tmpl
@@ -2,6 +2,22 @@
 */}}{{ if .Container }}{{ .Container.Id }}{{ else }}Obaly{{ end }}{{ end }}
 {{ define "Content" }}
 
+{{ if .ErrorNoSuchSeries }}
+<p>Chyba: Řada neexistuje.
+{{ else if .ErrorContainerAlreadyExists }}
+<p>Chyba: Obal s tímto ID už existuje.
+{{ else if .ErrorNoSuchContainer }}
+<p>Chyba: Obal neexistuje.
+{{ else if .ErrorCannotChangeSeriesNotEmpty }}
+<p>Chyba: Řadu u neprázdných obalů nelze měnit.
+{{ else if .ErrorCannotChangeNumber }}
+<p>Chyba: Číslo obalu v řadě nelze měnit.
+{{ else if .ErrorContainerInUse }}
+<p>Chyba: Obal se používá.
+{{ else if .Error }}
+<p>Chyba: {{ .Error }}
+{{ end }}
+
 {{ if .Container }}
 
 <section>
diff --git a/cmd/sklad/db.go b/cmd/sklad/db.go
index 0aba510..a6cdda8 100644
--- a/cmd/sklad/db.go
+++ b/cmd/sklad/db.go
@@ -14,6 +14,7 @@ import (
 type Series struct {
 	Prefix      string // PK: prefix
 	Description string // what kind of containers this is for
+	Counter     uint   // last used container number
 }
 
 func (s *Series) Containers() []*Container {
@@ -71,9 +72,6 @@ var (
 	labelFont *bdf.Font
 )
 
-// TODO: Some functions to add, remove and change things in the database.
-// Indexes must be kept valid, just like any invariants.
-
 func dbSearchSeries(query string) (result []*Series) {
 	query = strings.ToLower(query)
 	added := map[string]bool{}
@@ -110,6 +108,134 @@ func dbSearchContainers(query string) (result []*Container) {
 	return
 }
 
+var errInvalidPrefix = errors.New("invalid prefix")
+var errSeriesAlreadyExists = errors.New("series already exists")
+var errCannotChangePrefix = errors.New("cannot change the prefix")
+var errNoSuchSeries = errors.New("no such series")
+var errSeriesInUse = errors.New("series is in use")
+
+// Find and filter out the series in O(n).
+func filterSeries(slice []*Series, s *Series) (filtered []*Series) {
+	for _, series := range slice {
+		if s != series {
+			filtered = append(filtered, series)
+		}
+	}
+	return
+}
+
+func dbSeriesCreate(s *Series) error {
+	if s.Prefix == "" {
+		return errInvalidPrefix
+	}
+	if _, ok := indexSeries[s.Prefix]; ok {
+		return errSeriesAlreadyExists
+	}
+	db.Series = append(db.Series, s)
+	indexSeries[s.Prefix] = s
+	return dbCommit()
+}
+
+func dbSeriesUpdate(s *Series, updated Series) error {
+	// It might be easily possible with no members, though this
+	// is not reachable from the UI and can be solved by deletion.
+	if updated.Prefix != s.Prefix {
+		return errCannotChangePrefix
+	}
+	*s = updated
+	return dbCommit()
+}
+
+func dbSeriesRemove(s *Series) error {
+	if len(s.Containers()) > 0 {
+		return errSeriesInUse
+	}
+
+	db.Series = filterSeries(db.Series, s)
+
+	delete(indexSeries, s.Prefix)
+	delete(indexMembers, s.Prefix)
+	return dbCommit()
+}
+
+var errContainerAlreadyExists = errors.New("container already exists")
+var errNoSuchContainer = errors.New("no such container")
+var errCannotChangeSeriesNotEmpty = errors.New(
+	"cannot change the series of a non-empty container")
+var errCannotChangeNumber = errors.New("cannot change the number")
+var errContainerInUse = errors.New("container is in use")
+
+// Find and filter out the container in O(n).
+func filterContainer(slice []*Container, c *Container) (filtered []*Container) {
+	for _, container := range slice {
+		if c != container {
+			filtered = append(filtered, container)
+		}
+	}
+	return
+}
+
+func dbContainerCreate(c *Container) error {
+	if series, ok := indexSeries[c.Series]; !ok {
+		return errNoSuchSeries
+	} else if c.Number == 0 {
+		c.Number = series.Counter
+		for {
+			c.Number++
+			if _, ok := indexContainer[c.Id()]; !ok {
+				break
+			}
+		}
+		series.Counter = c.Number
+	}
+	if _, ok := indexContainer[c.Id()]; ok {
+		return errContainerAlreadyExists
+	}
+	if c.Parent != "" && indexContainer[c.Parent] == nil {
+		return errNoSuchContainer
+	}
+
+	db.Containers = append(db.Containers, c)
+
+	indexMembers[c.Series] = append(indexMembers[c.Series], c)
+	indexChildren[c.Parent] = append(indexChildren[c.Parent], c)
+	indexContainer[c.Id()] = c
+	return dbCommit()
+}
+
+func dbContainerUpdate(c *Container, updated Container) error {
+	newId := updated.Id()
+	if updated.Series != c.Series && len(c.Children()) > 0 {
+		return errCannotChangeSeriesNotEmpty
+	}
+	if updated.Number != c.Number {
+		return errCannotChangeNumber
+	}
+	if _, ok := indexContainer[newId]; ok && newId != c.Id() {
+		return errContainerAlreadyExists
+	}
+	if updated.Parent != c.Parent {
+		indexChildren[c.Parent] = filterContainer(indexChildren[c.Parent], c)
+		indexChildren[newId] = append(indexChildren[newId], c)
+	}
+	*c = updated
+	return dbCommit()
+}
+
+func dbContainerRemove(c *Container) error {
+	if len(indexChildren[c.Id()]) > 0 {
+		return errContainerInUse
+	}
+
+	db.Containers = filterContainer(db.Containers, c)
+	indexMembers[c.Series] = filterContainer(indexMembers[c.Series], c)
+	indexChildren[c.Parent] = filterContainer(indexChildren[c.Parent], c)
+
+	delete(indexContainer, c.Id())
+	delete(indexChildren, c.Id())
+	return dbCommit()
+}
+
 func dbCommit() error {
 	// Write a timestamp.
 	e := json.NewEncoder(dbLog)
diff --git a/cmd/sklad/main.go b/cmd/sklad/main.go
index fd675b1..5dc2174 100644
--- a/cmd/sklad/main.go
+++ b/cmd/sklad/main.go
@@ -7,6 +7,7 @@ import (
 	"log"
 	"math/rand"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
 	"time"
@@ -83,11 +84,40 @@ func handleLogout(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, "/", http.StatusSeeOther)
 }
 
-func handleContainer(w http.ResponseWriter, r *http.Request) {
-	if r.Method == http.MethodPost {
-		// TODO
+func handleContainerPost(r *http.Request) error {
+	id := ContainerId(r.FormValue("id"))
+	description := r.FormValue("description")
+	series := r.FormValue("series")
+	parent := ContainerId(r.FormValue("parent"))
+	_, remove := r.Form["remove"]
+
+	if container, ok := indexContainer[id]; ok {
+		if remove {
+			return dbContainerRemove(container)
+		} else {
+			c := *container
+			c.Description = description
+			c.Series = series
+			return dbContainerUpdate(container, c)
+		}
+	} else if remove {
+		return errNoSuchContainer
+	} else {
+		return dbContainerCreate(&Container{
+			Series:      series,
+			Parent:      parent,
+			Description: description,
+		})
 	}
-	if r.Method != http.MethodGet {
+}
+
+func handleContainer(w http.ResponseWriter, r *http.Request) {
+	var err error
+	if r.Method == http.MethodPost {
+		err = handleContainerPost(r)
+		// XXX: This is rather ugly. When removing, we want to keep
+		// the context id, in addition to the id being changed.
+	} else if r.Method != http.MethodGet {
 		w.WriteHeader(http.StatusMethodNotAllowed)
 		return
 	}
@@ -98,33 +128,70 @@ func handleContainer(w http.ResponseWriter, r *http.Request) {
 	}
 
 	var container *Container
-	children := []*Container{}
+	children := indexChildren[""]
 
-	if id := ContainerId(r.FormValue("id")); id == "" {
-		children = indexChildren[""]
-	} else if c, ok := indexContainer[id]; ok {
+	if c, ok := indexContainer[ContainerId(r.FormValue("id"))]; ok {
 		children = c.Children()
 		container = c
 	}
 
 	params := struct {
-		Container *Container
-		Children  []*Container
-		AllSeries map[string]string
+		Error                           error
+		ErrorNoSuchSeries               bool
+		ErrorContainerAlreadyExists     bool
+		ErrorNoSuchContainer            bool
+		ErrorCannotChangeSeriesNotEmpty bool
+		ErrorCannotChangeNumber         bool
+		ErrorContainerInUse             bool
+		Container                       *Container
+		Children                        []*Container
+		AllSeries                       map[string]string
 	}{
-		Container: container,
-		Children:  children,
-		AllSeries: allSeries,
+		Error:                           err,
+		ErrorNoSuchSeries:               err == errNoSuchSeries,
+		ErrorContainerAlreadyExists:     err == errContainerAlreadyExists,
+		ErrorNoSuchContainer:            err == errNoSuchContainer,
+		ErrorCannotChangeSeriesNotEmpty: err == errCannotChangeSeriesNotEmpty,
+		ErrorCannotChangeNumber:         err == errCannotChangeNumber,
+		ErrorContainerInUse:             err == errContainerInUse,
+		Container:                       container,
+		Children:                        children,
+		AllSeries:                       allSeries,
 	}
 
 	executeTemplate("container.tmpl", w, &params)
 }
 
-func handleSeries(w http.ResponseWriter, r *http.Request) {
-	if r.Method == http.MethodPost {
-		// TODO
+func handleSeriesPost(r *http.Request) error {
+	prefix := r.FormValue("prefix")
+	description := r.FormValue("description")
+	_, remove := r.Form["remove"]
+
+	if series, ok := indexSeries[prefix]; ok {
+		if remove {
+			return dbSeriesRemove(series)
+		} else {
+			s := *series
+			s.Description = description
+			return dbSeriesUpdate(series, s)
+		}
+	} else if remove {
+		return errNoSuchSeries
+	} else {
+		return dbSeriesCreate(&Series{
+			Prefix:      prefix,
+			Description: description,
+		})
 	}
-	if r.Method != http.MethodGet {
+}
+
+func handleSeries(w http.ResponseWriter, r *http.Request) {
+	var err error
+	if r.Method == http.MethodPost {
+		err = handleSeriesPost(r)
+		// XXX: This is rather ugly.
+		r.Form = url.Values{}
+	} else if r.Method != http.MethodGet {
 		w.WriteHeader(http.StatusMethodNotAllowed)
 		return
 	}
@@ -140,16 +207,30 @@ func handleSeries(w http.ResponseWriter, r *http.Request) {
 	if prefix == "" {
 	} else if series, ok := indexSeries[prefix]; ok {
 		description = series.Description
+	} else {
+		err = errNoSuchSeries
 	}
 
 	params := struct {
-		Prefix      string
-		Description string
-		AllSeries   map[string]*Series
+		Error                    error
+		ErrorInvalidPrefix       bool
+		ErrorSeriesAlreadyExists bool
+		ErrorCannotChangePrefix  bool
+		ErrorNoSuchSeries        bool
+		ErrorSeriesInUse         bool
+		Prefix                   string
+		Description              string
+		AllSeries                map[string]*Series
 	}{
-		Prefix:      prefix,
-		Description: description,
-		AllSeries:   allSeries,
+		Error:                    err,
+		ErrorInvalidPrefix:       err == errInvalidPrefix,
+		ErrorSeriesAlreadyExists: err == errSeriesAlreadyExists,
+		ErrorCannotChangePrefix:  err == errCannotChangePrefix,
+		ErrorNoSuchSeries:        err == errNoSuchSeries,
+		ErrorSeriesInUse:         err == errSeriesInUse,
+		Prefix:                   prefix,
+		Description:              description,
+		AllSeries:                allSeries,
 	}
 
 	executeTemplate("series.tmpl", w, &params)
diff --git a/cmd/sklad/series.tmpl b/cmd/sklad/series.tmpl
index 01e2539..0e31e0f 100644
--- a/cmd/sklad/series.tmpl
+++ b/cmd/sklad/series.tmpl
@@ -1,6 +1,20 @@
 {{ define "Title" }}{{ or .Prefix "Řady" }}{{ end }}
 {{ define "Content" }}
 
+{{ if .ErrorInvalidPrefix }}
+<p>Chyba: Neplatný prefix.
+{{ else if .ErrorSeriesAlreadyExists }}
+<p>Chyba: Řada s tímto prefixem už existuje.
+{{ else if .ErrorCannotChangePrefix }}
+<p>Chyba: Prefix nelze měnit.
+{{ else if .ErrorNoSuchSeries }}
+<p>Chyba: Řada neexistuje.
+{{ else if .ErrorSeriesInUse }}
+<p>Chyba: Řada se používá.
+{{ else if .Error }}
+<p>Chyba: {{ .Error }}
+{{ end }}
+
 {{ if .Prefix }}
 <h2>{{ .Prefix }}</h2>