Following a placebo washout period of 3-7 days, 251 hospitalized patients with a major depressive episode (DSM I11 and RDC criteria) were treated with either Org 3770 (20-60 mg/day) or amitnptyline (75-225 mg/day) for six consecutive weeks in this randomized, double-blind, multicentre study. Forty-one patients (19 Org 3770,22 amitriptyline) withdrew before completion of the 6-week active treatment period. In both groups, the main reason for withdrawal was lack of efficacy. However, fewer patients in the Org 3770 group than in the amitriptyline group withdrew as a result of adverse events (one and three patients, respectively). The severity of depressive symptoms and general psychopathology, as assessed by HPRSD (total and factors) and BPRS scales, improved to the same extent after 6 weeks' treatment with Org 3770 and amitriptyline. Similar improvement in global functioning, as assessed by GAS scale, was observed in both treatment groups. There were no statistically significant differences between the two treatments on all scales used. Dry mouth and sweating were reported significantly more often in the amitriptyline group. Other adverse events, such as constipation, dizziness, tremor and muscle weakness, occurred more frequently in the amitriptyline-treated patients as well. The results of this study indicate that Org 3770 has similar antidepressant efficacy to amitriptyline and a more favourable tolerability profile in patients with major depression.