This paper presents the results from a large multicenter study, performed at three clinical research units in the USA. Prior to a three to seven days of placebo washout period, patients were randomly assigned to zimelidine, a potent and selective 5-HT reuptake blocker, amitriptyline or placebo. The scheduled treatment period was four weeks. Dosage range was 75-300 mg/day for active medications. The rating instruments were the Hamilton Depression Scale and the Clinical Global Impression scale. The side effects were recorded by using a side effect inventory (TESS). Vital signs, laboratory work including clinical chemistry, ECG, and plasma levels of drugs, were performed. In the main efficacy evaluation there were 229 depressed outpatients included, all having completed at least two weeks of treatment after the washout period. The patients treated with zimelidine as well as those treated with amitriptyline showed a significant improvement relative to the placebo treated patients. For the safety evaluation 263 patients were included. Side effects, in particular anticholinergic effects but also drowsiness and cardiovascular effects, were much less pronounced in the zimelidine group as compared to the amitriptyline group. Only marginal differences regarding side effects were reported for zimelidine compared to those reported for placebo.