Moclobemide is a reversible monoamine oxidase inhibitor (MAOI) which preferentially inhibits type-A MAO. In the present communication the results obtained with moclobemide in various clinical trials are reviewed. To this day, the antidepressant efficacy of moclobemide has been compared to that of placebo in four trials. The antidepressant efficacy of moclobemide (300-600 mg/d; N = 164) was found to be superior to that of placebo (N = 162) and comparable to that of imipramine (100-200 mg/d; N = 164) in a 6-w., double-blind, multicentre study, in patients suffering from a Major Depressive Episode (DSM-III). Two smaller trials, strongly suggest that moclobemide is more efficacious than placebo for the treatment of endogenous depression (ICD-9) and for the treatment of Dysthymic Disorders (DSM-III). The antidepressant efficacy of moclobemide was compared to that of imipramine, desipramine, clomipramine and amitriptyline. The antidepressant efficacy of moclobemide (300-600 mg/d; N = 189) was found to be comparable to that of imipramine (100-200 mg/d; N = 192) in a 4-w., double-blind, multicentre study, in patients suffering from a Major Depressive Episode. This finding is supported by the results obtained in 12 other smaller studies, using either imipramine, desipramine, clomipramine or amitriptyline as comparator drug. When the tolerability of moclobemide, as judged by reported and observed adverse events, is compared to that of placebo, it appears that only nausea is reported significantly more frequently with moclobemide than with placebo (9.5% vs 4.8%). In the trials comparing moclobemide to tricyclic antidepressant drugs (TCAs), the tolerability of moclobemide was constantly found to be superior to that of the TCAs; in particular the incidence of anticholinergic side effects was low with moclobemide and was significantly higher with the TCAs. The cardiovascular tolerability of moclobemide tended to be superior to that of the TCAs. Physical examination, hematology and clinical chemistry did not seem to be affected by treatment in any of the studies summarized in this review.