Moclobemide was compared to placebo in two parallel groups of depressed patients, in a multicenter randomized, double-blind study of six weeks treatment duration. Forty seven patients participated in the study: 23 received moclobemide (flexible dose 300-600 mg/day) and 24 placebo. They were evaluated weekly for efficacy and tolerability. Moclobemide was more efficacious than placebo as judged by analysis on the total score on the Hamilton depression scale (p < 0.05) and by the overall assessment of efficacy (p < 0.01). Moclobemide was also more effective than placebo in the subgroup with neurotic depression (p < 0.05). In addition, the number of patients prematurely terminating treatment for inefficacy, was higher in the placebo than in the moclobemide group (12 versus 2, p < 0.01). The number and the severity of side-effects tended to be slightly greater in the moclobemide than in the placebo group, but this did not reach a level of significance. Cardiovascular tolerability was good in both treatment groups. No hypertensive crisis was reported. Hematology, clinical chemistry and urine analysis were not affected by the treatment in any clinically significant fashion.