The neuroendocrine responses to subcutaneous (SC) administration of the dopamine (DA) agonist apomorphine (APO) hydrochloride (0.75 mg) were studied in a large group of subjects: 110 drug-free inpatients with either DSM-III-R schizophrenia (SCZ, n = 46), schizoaffective disorder (SAD, n = 14), or major depressive episode (MDE, n = 50), plus 18 hospitalized controls. Compared to a saline test, APO induced a significant increase of growth hormone (GH), adrenocorticotropin (ACTH), and cortisol (COR) release and a decrease in prolactin (PRL) secretion. No change in thyrotropin (TSH) levels was observed. In the total sample the extents of ACTH, COR and GH responses were correlated, but in the group of 88 subjects who exhibit a normal GH stimulation this correlation disappeared. This discrepancy suggests that APO-induced ACTH and COR stimulation may be mediated by pathways different from those mediating GH stimulation. According to diagnostical categories, we found significant lower ACTH and COR stimulation in the schizophrenic group and in patients with SAD, compared with that among controls or depressed patients. We found also a significant difference between subgroups of schizophrenic patients. These results agree with the hypothesis that different aspects of psychosis might involve different subtypes of DA-receptors with different localizations and sensitivities.