Because of their low incidence of adverse effects SSRI are prescribed more and more frequently in patients with depressive disorders. SSRI inhibit different subsystems of cytochrome-P 450-oxydase. Especially during co-administration of SSRI with antipsychotic and antiarrhythmic drugs pharmacokinetic interactions have to be observed carefully. In this presentation a case of bradycardia after co-administration of paroxetine and metoprolol is reported. Drug history and a careful drug monitoring are necessary requirements to avoid serious adverse effects.