Moclobemide, a new reversible anti-MAO drug, was compared to imipramine in forty patients with major depression or dysthymic disorder. After a one-week wash-out period, patients were randomly allocated to the two treatment groups, receiving imipramine 25 mg tablets or Moclobemide 50 mg capsules for 28 days. Efficacy and tolerability were investigated by means of HRSD, CGI and VAS at baseline and thereafter at days 3, 7, 14 and 28. All patients completed the study, mean daily doses were 112.5 mg imipramine and 215 mg Moclobemide at day 28. Both treatments had similar antidepressant efficacy and a very good tolerability profile. Moclobemide was superior to imipramine in mean time to onset of effect (7.3 days versus 11.6 days: p less than 0.05) and in mean time to peak effect (13.5 days versus 18.5 days: 0.10 greater than p greater than 0.05. It is concluded that Moclobemide is a safe and effective anti-MAO drug, with an increasing rapid onset of therapeutic activity.