Metabolic reactions during long-time intravenous infusion of glucose in dosages according to basal energy requirements of man were investigated. Infusion of 0.2–0.4 g glucose/kg body weight/h led to the typical behaviour of blood glucose with an initial peak and a subsequent steady state. The steady state was dose-dependent and always higher than the starting value. Insulin always rose significantly with increasing scattering of the individual values with higher glucose loads. With 0.1 g glucose/kg/h, the steady state of blood glucose, after a minimal initial peak, was lower than the starting value, and no change of insulin in the peripheral venous blood could be observed.Free fatty acid levels initially always decreased, but rose again under low glucose loads (0.1 and 0.2 g/kg/h). In all experiments, with an increase of insulin, a decrease of serum potassium was found. Sodium, calcium, bilirubin, creatinine and urea-N did not show any typical change