Fluvoxamine, a selective serotonin reuptake inhibitor, was investigated in a 6-week double-blind study among severely ill inpatients with DSM-III major depression. All but 1 patient also fulfilled criteria for melancholia. Following a 3-day placebo wash-out patients were randomly assigned to fluvoxamine, imipramine or placebo. Sixty of 81 patients completed at least 2 weeks following wash-out and were evaluated for efficacy. Analysis of covariance (controlling for baseline scores) showed significant (p less than 0.05) differences on CGI severity and BPRS total and a similar trend (p = 0.08) on the Hamilton Depression Scale. Fluvoxamine was superior (p less than or equal to 0.02) to both placebo and imipramine on these measures. Fluvoxamine's most common adverse effects were nausea and agitation. The number of fluvoxamine patients withdrawn for side-effects was less than imipramine and not significantly different than placebo. Fluvoxamine was not associated with significant changes in vital signs, ECG or laboratory tests. The results therefore indicate that fluvoxamine is a safe and highly effective treatment for hospitalized patients with major depression.