90 patients between 18 and 65 years, with a DSM-III diagnosis of moderate or severe major depressive episode, were randomized to 6 weeks of treatment with Org 3770 or placebo in a double-blind trial. On main efficacy parameters, the 17-item HAMD, MADRS and CGI, Org 3770 was significantly superior to placebo (P < or = 0.05) in weeks 1-4 and at endpoint and recommended as continuation treatment to significantly more patients. The tolerability of Org 3770 was good: the only significant differences as compared with placebo were in the incidences of somnolence and increased appetite. The results show that Org 3770 is an effective and well-tolerated drug for the treatment of major depressive disorder.