We investigated the effects of exercise on hemodynamics and urinary protein excretion in 15 patients with early-stage diabetic nephropathy (DN) as compared the findings with these of 16 healthy volunteers. Patients were divided into two groups according to their renal histopathologic findings; Group D0 consisted of 8 patients in whom light microscopy showed minor glomerular abnormalities and Group DI consisted of 7 patients with early stage diffuse lesions. The subjects exercised on a treadmill at a workload of 4.7 METS for 20 minutes. Systolic blood pressure, heart rate and the pressure rate product were significantly higher in the DI group than in the D0 and control groups during exercise. Diastolic blood pressure was similar among the three groups. Creatinine clearance was unchanged during exercise. Urinary albumin excretion, urinary acid soluble protein excretion and urinary alpha 1-microglobulin excretion were all significantly increased in group DI compared with the D0 and control groups. Excretion of beta 2-microglobulin and N-acetyl-beta-D-glucosaminidase activity were unchanged during exercise. Our findings suggest that this provocative exercise test is useful for diagnosing early-stage diabetic nephropathy.