In order to evaluate the functional activity of the tubero-infundibular dopaminergic system in polycystic ovary syndrome (PCOS), we analysed the prolactin (PRL) and thyrotropin (TSH) responses to the dopamine antagonist sulpiride. We studied 8 euthyroid women affected by PCOS and 7 normal women. The mean baseline PRL values were normal in both groups. After sulpiride administration the incremental area under the PRL profile in PCOS was significantly lower than in normal subjects (p < 0.01). The mean basal plasma TSH levels were significantly higher in the PCOS than in the control group (p < 0.01). After sulpiride administration the incremental area under the TSH profile was significantly lower in PCOS patients than in normal women (p < 0.01). The higher basal plasma levels of TSH, the blunted response of PRL and the lack of response of TSH to sulpiride in PCOS suggest a relative decrease of the dopaminergic activity in PCOS patients.