One hundred ninety-four nonmelancholic depressed outpatients with features of atypical depression took part in a 6-week randomized trial of imipramine hydrochloride, phenelzine sulfate, and placebo. Their courses of illness were also rated for chronicity. Significantly more patients responded to phenelzine (71%) than to imipramine (48%), which benefited significantly more patients than placebo (26%). Both chronicity and DMS-III diagnosis predicted response on several outcome measures. For example, patients with dysthymic disorder responded better to treatment than did those with major depression, suggesting that dysthymic disorder can be treated with medication. Placebo response correlated inversely with chronicity, regardless of DMS-III diagnosis. Atypical depression and longitudinal course of illness may add to the usefulness of DMS-III depressive diagnosis as a predictor of antidepressant response.