We performed a follow-up study of the glomerular function in a series of 29 Type 1 (insulin-dependent) diabetic patients who had been studied 18 years previously. Initial median duration of diabetes was 2 years (range 0-9) and at follow-up 21 (17-27) years. At follow-up, 8 diabetic patients exhibited increased urinary albumin excretion rate 515 (32-3234) micrograms/min with glomerular filtration rates significantly lower than 21 diabetic patients with normal urinary albumin excretion (85 vs 126 ml/min/1.73 m2; p less than 0.01). The patients with increased urinary albumin excretion rate also had higher arterial blood pressure (145/90 vs 120/80) mm Hg; p less than 0.02) and increased frequency of proliferative retinopathy (7 out of 8 vs 2 out of 21; p = 0.0001) as compared to the group with normal urinary albumin excretion. However, we found no association of increased urinary albumin excretion rate (incipient or overt nephropathy) to early glomerular hyperfiltration as median initial glomerular filtration rate was 142 ml/min/1.73 m2 in the diabetic patients with increased urinary albumin excretion and 147 ml/min/1.73 m2 in the patients with normal excretion rate (p greater than 0.05).