Purpose. This study investigates the role of insulin in retinal function by examining the effects of insulin on the a- and b-waves of the electroretinogram (ERG) recorded from anin vitrobovine retina eye-cup preparation.Methods. Bovine eyes were enucleated immediately after exsan-guination, hemisected to form an eye cup, and transported to the laboratory in oxygenated medium. Eye cups were then transferred to a perfusion system that provided constant superfusion of oxygenated perfusate solution to the retina, enabling it to remain in a functional statein vitro. The ERG was recorded, as the retinal response to photic stimulation, from electrodes mounted within the perfusion system. The effects of insulin on the ERG were investigated by adding insulin to the perfusate solution.Results. Application of insulin to thein vitroretina preparation decreased the amplitudes of the a- and b-waves of the ERG in a dose dependent manner with a maximal effect at doses of 0.1 U/ml and above. These effects were reversible.Conclusion. The reduction of ERG amplitudes may result from the hyperpolarising effect of insulin reported in other tissues. The findings suggest that insulin may have a regulatory role in retinal activity; however extrapolation of these results to the intact organism is dependent on the presence of insulin in retina.