Patients were eligible if they had best corrected visual acuity of 20/100 or better in each eye and the presence of proliferative diabetic retinopathy in at least one eye or severe nonproliferative retinopathy in both eyes. They could not have had prior treatment with photocoagulation or pituitary ablation, and both eyes had to be suitable for photocoagulation. All eligible patients were younger than 70 years, and the examining physician assessed the outlook for survival and availability for 5 years of followup to be good.