The neuroendocrine challenge test is a useful way of examining the functional integrity of the monoamine pathways that control the secretion of pituitary hormones. The 5-HT uptake inhibitor clomipramine has a considirable use as a 5-HT challenge test. Serotonergic systems in the brain are often disturbed in depressed patients and the role of serotonin in schizophrenia is still unclear. Serotonin is an effective stimulator of prolactine and cortisol release. In this study, we investigated the activity of serotonergic system in depressive and schizophrenic patients via serum plolactin and cortisol levels stimulated by the clomipramine challenge test. While the prolactin /DeltaEmax responses of the depressed and schizophrenia patients to clomipromine tended to be significantly different, the difference between responses of cortisol /DeltaEmax was not statistically significant. We believe that this study gives quite reliable results relating to the serotonergic system; even though the total number of cases was small, the placebo and clomipramine test results of each patient were compared. This study has two important results 1) The cortisol and prolactin responses to clomipramine are more predictive in depression than schizophrenia cases 2) Depressives give more active responses to serotonergic stimulations.