Nefazodone is a phenylpiperazine antidepressant with 5-HT2 antagonism and 5-HT reuptake inhibition. Two hundred and eighty-three out-patients with a diagnosis of DSM-III-R major depression of at least one-month duration (65% ill for over 6 months), and a mean score of 24 on the 17-item Hamilton Rating Scale for Depression (HRSD), were randomised to treatment with nefazodone, imipramine, or placebo. The double-blind treatment period was 8 weeks in duration. Nefazodone's antidepressant efficacy was comparable with imipramine's, with both drug treatments significantly better than placebo in a variety of outcome measures. For example, after 8 weeks of therapy, 78% of nefazodone and 83% of imipramine but only 55% of placebo patients (P < 0.01) were globally much or very much improved. Nefazodone was better tolerated than imipramine, with fewer drop-outs and a lower incidence of side-effects during treatment.