The present study was undertaken in order to evaluate the acute metabolic and hormonal effects of human growth hormone in healthy subjects. Glucose turnover, plasma glucose, FFA, insulin, C-peptide, glucagon, and somatostatin concentrations were determined in the fasting state after a bolus injection of placebo or growth hormone in quantities producing increases in plasma growth hormone levels within the normal physiological range. We found that growth hormone administration resulted in negligible changes in plasma glucose, no significant changes in appearance or disappearance rates of glucose, a moderate increase in FFA and a moderate fall in plasma insulin, C-peptide and glucagon concentrations, while plasma somatostatin levels were unchanged. These findings suggest that rapid changes in plasma growth hormone concentrations, corresponding to the fluctuations seen during normal daily life, may play a role in the short time regulation of blood glucose concentration through an inhibition of insulin and glucagon secretion.