Based on the results of an open trial with Ro 8-1998 (chemic name: N,N-dimethyl-3-(1-methyl-5H-dibenzo(a,d)cycloheptene-5-ylidene)-propylamine N-oxide hydrochloride) in 11 endogenous depressed outpatients a double-blind trial with imipramine was proposed. Therapeutic efficacy and side effects of Ro 8-1998 and imipramine were compared in a double-blind trial with 30 patients who were newly hospitalized. Most of them suffered from endogenous depression. On days 0, 5, 10, 15 and 20 the patients were examined and the symptoms were documented with the AMP system, the Hamilton scale for depression, a behaviour rating and the "global depression rating Zurich". Ro 8-1998 caused a decrease of systolic blood pressure, an increase of heart frequency and urea. Twelve out of 15 patients showed a decrease of white blood cells. In four patients the number of white blood cells dropped below 4,000. Statistical analyses proved both substances to be potent antidepressants. The therapeutic efficacy of Ro 8-1998 was at least equal to that of imipramine. Further trials with bigger groups of patients are necessary to show whether the trend towards a better antidepressant efficacy of Ro 8-1998 can be reproduced.