Glomerular filtration rate (GFR) as assessed by endogenous creatinine clearance was studied in 46 male and 38 female patients with diabetes mellitus (DM). Of these, 44 patients had uncomplicated DM (Group I) whilst 40 patients had complicated DM (Group II). There were 20 insulin-dependent diabetes mellitus (IDDM) patients in Group I and 5 in Group II, and 24 non-insulin dependent diabetes mellitus (NIDDM) patients in Group I and 35 in Group II. In Group I, 6 IDDM and 4 NIDDM patients had supranormal glomerular filtration rate (creatinine clearance 125 ml/min) and in Group II 1 IDDM and 6 NIDDM patients had supranormal GFR. The presence of diabetic complications and the mode of therapy of the diabetic state did not significantly affect the glomerular filtration rate. This concludes that glomerular hyperfiltration occurred in both IDDM and NIDDM Nigerian patients.