Studies of the effect of sorbinil, an aldose reductase inhibitor, in human diabetic neuropathy have shown improvements in motor and sensory nerve conduction velocity and somatosensory evoked potentials, and a reduction in neuropathic pain. Improvements in motor and sensory deficits have also been detected clinically. These effects occurred after the administration of sorbinil for relatively short periods. However, more prolonged treatment may be necessary to achieve a therapeutic response in some patients. The results of tests of cardiac autonomic (vagal) function improved with the administration of sorbinil for 6 weeks. The most notable finding was a reduction in resting heart rate. Improvements in both clinical and test measures, related to autonomic and somatic nerve function, have reversed on withdrawal of sorbinil and improved again on renewal of administration. Toxic manifestations of sorbinil were infrequent, almost invariably mild, and readily reversible.