The role of dopaminergic ways in human copulatory activity and the high frequency of impotence in diabetes mellitus are well known. In order to study the involvement of the central dopaminergic tone in diabetic impotence we have evaluated the PRL and TSH response to metoclopramide (MCP 10 mg ev) in 28 diabetic male patients (15 ID including 6 impotent and 13 NID including 5 impotent ) compared with 9 healthy controls. All subjects were investigated for the presence of neuropathy, retinopathy, macroangiopathy, gonadal and thyroid diseases. The PRL response to MCP was greater (p less than 0.05) in impotent patients than in controls at 60' and 90' in ID, and at 30' and 120' in NID. There was no significant difference in TSH increase and in PRL and TSH response areas between the groups considered. In conclusion, the dopaminergic tone is substantially normal in diabetic patients, while some PRL hyperresponsiveness to MCP exists in impotent diabetics.