The antidepressive efficacy of 1-deprenyl (5-10 mg daily) plus 1-phenylalanine (250 mg/day) has been evaluated in 155 unipolar depressed patients. Both oral and intravenous administration showed beneficial effects in 90% of outpatients and 80.5% of inpatients. It is concluded that this combined treatment has a potent antidepressive action based on the accumulation of 1-phenylethylamine in the brain.