Photopic, 30-Hz, and foveal electroretinograms were measured in 19 diabetic patients in an experimental study of the effects of short-term Sorbinil (an aldose-reductase inhibitor) on retinal function. Patients were assigned in double-blind fashion to Sorbinil (250 mg/day) or placebo groups and were tested at the outset and after four weeks of therapy. Comparisons (t-test) between the Sorbinil and placebo groups failed to show significant effects of treatment on electroretinograms, although there was a significant correlation within the Sorbinil group between foveal recordings and red cell sorbitol at the end of treatment. Analysis showed that increased foveal electroretinograms were found in patients with low initial retinopathy but not in those with greater retinopathy. Eight patients continued Sorbinil treatment for one year. Again patients improving their foveal measurements had less initial retinopathy than those not improving. This difference was significant after one year of treatment but not at four weeks.