The influence of glycine, the simplest amino acid, on pituitary function has been investigated in the present study. Different doses (4, 8, or 12 g) of glycine were intravenously infused over 15 or 30 min in normal subjects. Serum levels of GH (growth hormone) and Prl (prolactin) were measured before and after the infusion, and also blood sugar levels were determined. The dose of 4 or 8 g glycine induced a significant increase in serum GH (P less than 0.05 or P less than 0.001, respectively); however, a more pronounced and significant increase in serum GH levels was observed after infusion at a dose of 12 g glycine (P less than 0.001). It was clearly observed that the dose-dependent GH release to intravenous glycine occurred in normal subjects. On the contrary, serum Prl level was not changed significantly, and blood sugar level was transiently, but significantly (P less than 0.05), increased after the infusion of 12 g glycine. The present data suggest that glycine might play an important role in the control of hypothalamic-pituitary function.