Brofaromine (CGP 11 305 A), a new reversible and selective MAO-A inhibitor, was studied in two multicentre, (Trial A and Trial B) double-blind, dose-finding trials in a total of 124 depressed in-patients. Doses of 25, 50 and 75 mg bid were compared, to determine which was the most effective. The duration of the trials was four weeks. The comparative drugs were nomifensine (100 mg/day) and tranylcypromine (20 mg/day). The majority of patients in the Trial A was classified as "endogenous" depression. Diagnosis of depression was based on DSM-III or ICD-9 criteria. Conversely, most of the patients in Trial B were "non-endogenous" depressives. In "endogenous" depression, a statistically significant linear dose-response relationship was found in all the efficacy variables assessed. The most effective dose was 150 mg/day. This dose gave a mean drop of 25.3 +/- 11.9 (S.D.) points in the total Hamilton Depression Rating Scale (HAMD) scores and provided successful treatment in 83% of the patients treated, success being defined as a drop of at least 50% in the initial HAMD score at the end of the trial period. In "non-endogenous" depression, no statistical difference was found between the four treatment groups in any of the efficacy variables assessed. Response rate in all brofaromine groups averaged 59% (tranylcypromine group 60%). Tolerability was good in 90% or more of the brofaromine patients in both trials, regardless of the dose administered. The side effects reported most frequently were sleep disturbances, nausea, and headaches.