Antidepressant drugs in the treatment of chronic depressions have received little systematic study. We used a two-week, single-blind placebo washout followed by a six-week, double-blind comparison of imipramine hydrochloride and placebo in a sample of 76 outpatients with DSM-III dysthymic disorder entered into a trial at two centers. Subjects were preponderantly female, had insidious onset at an early age, and had depressions of moderate severity; 96% also met the DSM-III criteria for major depressive disorder at the time of presentation. Sixty percent had a history of persistent depressive symptoms sufficient to meet criteria for major depression for longer than two years. Markedly favorable responses occurred in 45% of imipramine-treated (n = 29) and 12% of placebo-treated (n = 25) patients and, respectively, 59% and 13% of those who completed the study. Imipramine produced significant advantage in measures of depressive symptoms, global severity of illness, and self-rated social and vocational function. Recovered patients experienced remission from both long-standing symptoms and deficits as well as more recently exacerbated aspects of their syndrome. Patients with pure dysthymic disorder of a mild, subsyndromal type were uncommon in these clinical settings. However, anti-depressant medication was effective for many moderately severe chronic depressions, which had previously been untreated or undertreated, presumably related to misdiagnosis.