diff --git a/pkg/obidefault/progressbar.go b/pkg/obidefault/progressbar.go
index 3bce334..d752525 100644
--- a/pkg/obidefault/progressbar.go
+++ b/pkg/obidefault/progressbar.go
@@ -1,5 +1,7 @@
 package obidefault
 
+import "os"
+
 var __no_progress_bar__ = false
 
 func ProgressBar() bool {
@@ -17,3 +19,22 @@ func SetNoProgressBar(b bool) {
 func NoProgressBarPtr() *bool {
 	return &__no_progress_bar__
 }
+
+// ProgressBarVisible tells whether a progress bar can be displayed: it is not
+// disabled by --no-progressbar, the standard error output is a terminal and
+// the standard output is not piped to another command.
+func ProgressBarVisible() bool {
+	if !ProgressBar() {
+		return false
+	}
+
+	if e, err := os.Stderr.Stat(); err != nil || (e.Mode()&os.ModeCharDevice) != os.ModeCharDevice {
+		return false
+	}
+
+	if o, err := os.Stdout.Stat(); err == nil && (o.Mode()&os.ModeNamedPipe) == os.ModeNamedPipe {
+		return false
+	}
+
+	return true
+}
diff --git a/pkg/obigraph/clique.go b/pkg/obigraph/clique.go
index 8572dc0..3297f18 100644
--- a/pkg/obigraph/clique.go
+++ b/pkg/obigraph/clique.go
@@ -21,6 +21,10 @@ type CliqueOptions struct {
 	Workers int
 	// Seed seeds the random vertex orders of the restarts.
 	Seed int64
+	// Progress, if set, is called with the size of the best clique each time a
+	// larger one is found. Calls are serialized and made while a lock is held:
+	// it must return quickly and must not call FindClique.
+	Progress func(best int)
 }
 
 // CliqueResult is the outcome of FindClique.
@@ -68,6 +72,9 @@ func FindClique(ctx context.Context, n int, filter NeighborFilter, target int, o
 		mutex.Lock()
 		if len(clique) > len(best) {
 			best = append(best[:0], clique...)
+			if opts.Progress != nil {
+				opts.Progress(len(best))
+			}
 		}
 		mutex.Unlock()
 	}
diff --git a/pkg/obigraph/clique_test.go b/pkg/obigraph/clique_test.go
index b2c6cd2..0d9f0ad 100644
--- a/pkg/obigraph/clique_test.go
+++ b/pkg/obigraph/clique_test.go
@@ -141,3 +141,23 @@ func TestFindCliqueTimeout(t *testing.T) {
 		t.Fatalf("invalid best clique %v", r.Clique)
 	}
 }
+
+func TestFindCliqueProgress(t *testing.T) {
+	adj := randomGraph(rand.New(rand.NewSource(4)), 40, 0.7)
+
+	var seen []int
+	r := FindClique(context.Background(), 40, matrixFilter(adj), 5, CliqueOptions{
+		Progress: func(best int) { seen = append(seen, best) },
+	})
+	if !r.Reached {
+		t.Fatalf("size 5 should be reached: %+v", r)
+	}
+	if len(seen) == 0 || seen[len(seen)-1] != len(r.Clique) {
+		t.Fatalf("progress %v does not end at the clique size %d", seen, len(r.Clique))
+	}
+	for i := 1; i < len(seen); i++ {
+		if seen[i] <= seen[i-1] {
+			t.Fatalf("progress must be strictly increasing: %v", seen)
+		}
+	}
+}
diff --git a/pkg/obitools/obioligotag/obioligotag.go b/pkg/obitools/obioligotag/obioligotag.go
index bb3e93b..bd6dbd7 100644
--- a/pkg/obitools/obioligotag/obioligotag.go
+++ b/pkg/obitools/obioligotag/obioligotag.go
@@ -163,8 +163,14 @@ func CLIOligoFamily() ([]string, error) {
 	}
 
 	filter := obikmer.NewKmerDissimilarityFilter(kmers, size, metric, dmin)
+	progress := startCliqueProgress(target)
 	result := obigraph.FindClique(ctx, len(kmers), filter, target,
-		obigraph.CliqueOptions{Workers: obidefault.ParallelWorkers(), Seed: 1})
+		obigraph.CliqueOptions{
+			Workers:  obidefault.ParallelWorkers(),
+			Seed:     1,
+			Progress: progress.Update,
+		})
+	progress.Stop(result.Reached)
 
 	switch {
 	case result.Reached:
diff --git a/pkg/obitools/obioligotag/progress.go b/pkg/obitools/obioligotag/progress.go
new file mode 100644
index 0000000..bcf5208
--- /dev/null
+++ b/pkg/obitools/obioligotag/progress.go
@@ -0,0 +1,86 @@
+package obioligotag
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/schollz/progressbar/v3"
+
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obidefault"
+)
+
+// cliqueProgress displays the progress of the search of a family: the bar goes
+// from 0 to the required family size and follows the size of the best family
+// found so far. A nil *cliqueProgress does nothing, which is what is used when
+// no progress bar has to be displayed.
+type cliqueProgress struct {
+	bar  *progressbar.ProgressBar
+	max  int
+	stop chan struct{}
+	done sync.WaitGroup
+}
+
+// startCliqueProgress starts the progress bar of a search for a family of
+// target oligonucleotides, or returns nil if no bar can be displayed.
+func startCliqueProgress(target int) *cliqueProgress {
+	if !obidefault.ProgressBarVisible() {
+		return nil
+	}
+
+	p := &cliqueProgress{
+		max:  target,
+		stop: make(chan struct{}),
+		bar: progressbar.NewOptions(target,
+			progressbar.OptionSetWriter(os.Stderr),
+			progressbar.OptionSetWidth(15),
+			progressbar.OptionShowCount(),
+			progressbar.OptionSetElapsedTime(true),
+			progressbar.OptionSetPredictTime(false),
+			progressbar.OptionThrottle(100*time.Millisecond),
+			progressbar.OptionSetDescription("[Searching a family of oligonucleotides]"),
+		),
+	}
+
+	// The search may stay a long time on the same family: keep the elapsed
+	// time alive.
+	p.done.Add(1)
+	go func() {
+		defer p.done.Done()
+		ticker := time.NewTicker(500 * time.Millisecond)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				p.bar.Add(0)
+			case <-p.stop:
+				return
+			}
+		}
+	}()
+
+	return p
+}
+
+// Update reports the size of the best family found so far.
+func (p *cliqueProgress) Update(best int) {
+	if p != nil {
+		p.bar.Set(min(best, p.max))
+	}
+}
+
+// Stop ends the display. The bar is filled only if the family was found.
+func (p *cliqueProgress) Stop(reached bool) {
+	if p == nil {
+		return
+	}
+	close(p.stop)
+	p.done.Wait()
+	if reached {
+		p.bar.Finish()
+	} else {
+		p.bar.Exit()
+	}
+	fmt.Fprintln(os.Stderr)
+}