Partial sleep deprivation (PSD) has a profound and rapid effect on depressed mood. However, the transient antidepressant effect of PSD - most patients relapse after one night of recovery sleep—is limiting the clinical use of this method. Using a controlled, balanced parallel design we studied, whether repetitive transcranial magnetic stimulation (rTMS) applied in the morning after PSD is able to prevent this relapse. 20 PSD responders were randomly assigned to receive either active or sham stimulation during the following 4 days after PSD. Active stimulation prolonged significantly (p<0.001) the antidepressant effect of PSD up to 4 days. This finding indicates that rTMS is an efficacious method to prevent relapse after PSD.