Eight patients with established insulin-dependent diabetes mellitus were studied before and 2 weeks after the initiation of pumped continuous sc insulin infusion in order to investigate the effect of short term improvement of glycemic control on hormonal and lipid levels. Glycemic control was improved in all patients. Using a constant blood withdrawal pump, accurate 24-h average concentrations, denoted integrated concentrations, were obtained. The mean 24-h integrated concentrations of GH, cortisol, norepinephrine, and epinephrine did not change significantly. The mean fasting triglyceride concentration dropped from 119.1 to 83.4 mg/dl (P less than 0.05). The mean 24-h integrated concentration of plasma triglycerides fell from 132.1 to 101.5 mg/dl (P less than 0.02). Both mean fasting and mean 24-h integrated concentrations of plasma cholesterol were lower after improved control. Short term improvement in glycemic control was associated with a reduction in plasma lipid concentrations, but failed to alter mean 24-h integrated concentrations of the measured counterregulatory hormones.