The effect of 250 mg day-1 of the aldose reductase inhibitor, Sorbinil, upon peripheral nerve function was assessed in 23 adult diabetics with clinical neuropathy. Sorbinil was given for 4 weeks to 10 subjects, while 13 received placebo in this double-blind study. Open label treatment with Sorbinil was then continued for 52 weeks in 10 of the 23 subjects. Red cell sorbitol, hemoglobin A1c, vibratory sensation, median nerve sensory and motor conduction velocities were measured at 0, 4 and 52 weeks. There were no measurable changes in peripheral nerve function after 4 weeks of Sorbinil treatment. After 52 weeks significant improvement was found in the median nerve motor and sensory conduction velocities. This was associated with no change in blood glucose control but a reduction of erythrocyte sorbitol levels.