Two matched groups of insulin requiring non-insulin dependent diabetic (NIDDM) patients with mild proteinuria (200 to 999 mg/day), one on mono component (MC) insulin therapy and the other on conventional insulins were studied for a 3 year period to evaluate the course of nephropathy in these two groups. Twenty-seven and 35 patients were followed-up in the MC insulin and conventional insulin groups respectively. In the MC insulin treated group, the percentage of patients showing deterioration in proteinuria was lower (11% vs 34%, P less than 0.05) and the percentage showing improvement was higher (48% vs 29%) compared to the conventional insulin treated group. Insulin antibody titres decreased significantly in the MC insulin group and serum C-peptide values decreased in both groups on follow-up.