A relative deficiency in dopamine has been suggested to explain the inappropriate gonadotropin secretion and postulated increased GnRH secretion characteristic of polycystic ovary syndrome (PCO). Previous studies demonstrated an exaggerated decrement in serum LH after large iv doses of dopamine (DA, 4-5 micrograms/kg X min). Normoprolactinemic patients with PCO and weight- and estrogen-matched normal women received iv infusions of DA in two doses (0.5 and 4 micrograms/kg X min). After DA, each subject also received iv metoclopramide (MCP; 10 mg). Serum LH decreased (P less than 0.05) during DA infusion to a similar degree in PCO [23 +/- 3% (+/- SE)] and normal women (20 +/- 2%). In PCO patients, the decrease in LH was similar with both DA doses. Serum PRL and TSH responses to DA were also similar in PCO and normal women. After MCP treatment, serum LH did not change, but serum PRL increased more in PCO (801 +/- 100%) than in normal women (467 +/- 73%; P less than 0.05), as did serum TSH. These data suggest that the sensitivity of LH to DA in patients with PCO is not increased. Further, increased responses of PRL and TSH to MCP may reflect increased dopaminergic activity or, in the case of PRL, the influence of chronic hyperestrogenism.