Dothiepin, a well-established antidepressant, has been compared with clomipramine in a single-blind study which demonstrated that dothiepin was better tolerated but there was no difference in efficacy. The present study was performed to recent European guidelines on good clinical practice using a randomised, double-blind, parallel-group methodology. One hundred and one patients suffering from major depressive disorder as defined by DSM-III-R were randomised to receive either clomipramine (25-150 mg daily) or dothiepin (75-150 mg daily) for up to six weeks. The clomipramine group comprised 51 patients, the dothiepin group 50 patients. At baseline, both groups had a mean age of 41-43 years and gave similar mean scores on the Hamilton Depression Rating Scale (23.5 for clomipramine, 23.6 for dothiepin). At endpoint it was reduced in both groups but there were no significant differences between the groups (mean change from baseline for the clomipramine and dothiepin groups was -14.6 and -14.1 respectively). Thirty-one clomipramine patients and 41 dothiepin patients completed six weeks' treatment. Withdrawal from treatment (20 patients for clomipramine, nine for dothiepin) was significantly different (p = 0.0105). When reasons for withdrawal were analysed, 13 clomipramine patients and two dothiepin patients withdrew because of adverse events, this difference being significant (p = 0.002). Thus both treatments were effective in treating patients suffering from major depressive disorder, but patients receiving dothiepin suffered fewer adverse events and were more likely to complete their treatment.