The stimulatory effects of growth hormone (GH) and glucagon on renal function are well known, but it is uncertain whether these hormones are involved in the increase in renal function, characteristic of type 1 (insulin-dependent) diabetes mellitus. Therefore, the circulatory levels of GH and glucagon were measured in 10 type 1 diabetic patients with an elevated glomerular filtration rate (GFR > 130 ml min-1 1.73 m-2) and in 20 age and sex matched normofiltering patients (GFR ranging from 90-130 ml min-1 1.73 m-2). In the patients, fasting glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were determined using 125I-iothalamate and 131I-hippuran, respectively, during near-normoglycaemia. On a separate day, the levels of glucagon and GH were determined in the fasting basal state and after exercise. Multiple regression analysis disclosed that GFR was positively correlated with HbA1 (r2 = 0.18, p < 0.01), glucagon (r2 = 0.14, p < 0.03) as well as exercise-stimulated GH (r2 = 0.10, p < 0.05). ERPF was independently associated with HbA1 (r2 = 0.24, p < 0.005) and glucagon (r2 = 0.18, p < 0.01), whereas renal vascular resistance (RVR) was negatively correlated with stimulated GH (r2 = 0.18, p < 0.02). Kidney volume was positively correlated with HbA1 (r2 = 0.26, p < 0.001) and inversely with RVR (r2 = 0.16, p < 0.01), but not with glucagon or stimulated GH. The present study suggests that circulatory GH and glucagon play a contributory role in the renal haemodynamic changes in type 1 diabetes mellitus.