This study has been conducted on 17 patients suffering from neurotic and psychotic depressions, who had not received a pharmacological antidepressive therapy since at least 1 month. 6 patients suffering from psychotic depression were treated with 100 mg clomipramine i.v. daily for 20 days; 11 patients, 7 of whom suffered from psychotic depression and 4 from neurotic depression, were treated with 150 mg maprotiline i.v. daily for 20 days. In both groups the therapy has been continued orally. In 17 patients a remarkable improvement and even in some cases complete recovery has been obtained. The two psychotropic antidepressive drugs are, furthermore, both active in the same symptoms. The determination of serotonin in human platelets confirms the strong inhibition of its re-uptake by clomipramine and the absence of re-uptake of 5-HT with maprotiline. A constant and progressive increase of 5-HIAA was noted in patients treated with clomipramine. This increase may be considered as a consequence of the increased metabolism of the larger quantitity of 5-HT used by the central synapses. The interpretation of the increased levels of 5-HIAA in patients treated with maprotiline is more difficult. Further trials, for instance on the plasmatic tryptophan level, will perhaps solve the problem.