Growth hormone and cortisol secretion were studied in 25 patients with insulin-dependent diabetes before (Study 1) and 2 weeks after improved glucoregulation (Study 2). Blood samples for serum growth hormone (GH) and blood glucose determination were collected at hourly intervals whilst blood samples for cortisol and C-peptide were collected every 6 h during the 24-h period in Study 1 and Study 2. Glycaemic control was significantly improved in Study 2 compared to that in Study 1 (8.5 vs 13.3 mmol/l; P less than 0.001). With improved control, growth hormone levels rose by 21% (5.7 vs 4.7 mU/l; P less than 0.05). Throughout both study periods growth hormone levels were higher in patients with no residual C-peptide secretion (10 CpN patients) compared with patients with residual beta-cell function (15 CpP patients) (7.1 vs 3.2 mU/l in Study 1; 8.9 vs 4.2 mU/l in Study 2; P less than 0.001). Characteristic shapes of the 24-h blood glucose profile curves during both study periods were significantly different between the CpN and CpP group. Plasma cortisol decreased in both groups with improved metabolic control (P less than 0.001) but the observed different diurnal pattern did not change. These results demonstrate the importance of residual endogenous insulin secretion in determining growth hormone secretion in insulin-dependent diabetes and have important implications for glycaemic control and risk of microvascular complications.