Dopamine in humans inhibits the secretion of luteinizing hormone (LH), follicular stimulating hormone (FSH), thyroid stimulating hormone (TSH) and prolactin (PRL), and is a stimulator of growth hormone (GH) secretion. Dopamine-D1 receptor stimulation with fenoldopam increases basal PRL levels, suppresses TSH, and increases gonadotropin releasing hormone (LHRH) induced LH release. We have investigated the effect of a dopamine D1-receptor antagonist, NNC 01-0687, on the secretion of anterior pituitary hormones. In 8 healthy males NNC 01-0687 and placebo were administered orally in a double-blind placebo controlled cross-over study for three days with a wash-out period of 14 days. Hormonal responses (PRL, LH, FSH, GH, TSH, thyroid hormones and testosterone), unstimulated and LHRH/TRH stimulated, were studied on days 1 and 3. No significant difference (p > 0.05) between placebo and active periods was found neither in unstimulated nor in stimulated hormone concentrations expressed in absolute values, percent change of before, incremental values and area under the curve. These results suggest that the neuronal DA-D1 activity is not activated during basal conditions in healthy male subjects.