We examined 178 men for the presence of diabetic retinopathy during 1978-80. They had been part of a group of 205 men from the Jerusalem area, diagnosed as being diabetic or having an abnormal glucose tolerance test in the Israel Ischaemic Heart Disease Project, a 5-year epidemiological investigation of Israeli male government employees. Seventy-four (42%) had diabetic retinopathy as determined by direct and indirect ophthalmoscopy, 3-mirror contact lens examination, and fundus photography. Those with and without retinopathy were compared for clinical, biochemical, behavioural, and biographical variables measured subsequently in 1963, 1965, and 1968. We found no significant differences between the 2 groups with respect to antecedent Quetelet index, blood pressure, peripheral vascular disease, blood lipids, haematocrits, smoking habits, area of birth, and education. Statistically significant differences between men with and without retinopathy were found for severity of carbohydrate metabolic intolerance at identification, duration of the metabolic abnormality, age, casual glucose values, and serum uric acid levels. Low serum uric acid appears to precede the incidence of diabetic retinopathy and to decline further as the disease progresses.