The effect of imidazole-2-hydroxibenzoate on urinary excretion rates of glycosaminoglycans and albumin in 22 insulin-dependent diabetics with albumin excretion rates under 300 mg/day was evaluated in a 165-day double blind crossover study. Unlike placebo, the drug reduced glycosaminoglycan and albumin excretion rates significantly after 40 and 60 days of treatment, and the effects were significantly intercorrelated. Moreover, a parallel reduction in urinary excretion of N-acetyl-beta-D-glucosaminidase was also observed. These pharmacological effects may have a positive impact on the subsequent natural history of diabetic nephropathy.