To assess the quality of screening for diabetic retinopathy by 19 general practitioners (GPs) using ophthalmoscopy, the GPs' performance was compared with the performance of ophthalmologists. The GPs had received special training in retinal examination. Direct ophthalmoscopy was performed after mydriasis of both eyes. Later, one of the ophthalmologists at the local hospital performed ophthalmoscopy in the same way as the GP. The ophthalmologist's diagnosis was used as the criterion for retinopathy. 252 NIDDM patients were analysed. The ophthalmologists found 23 cases of retinopathy, of which one patient was referred immediately for photocoagulation. The GPs diagnosed 12 and missed 11 of these 23 cases (false negatives): sensitivity 52%. In 37 of the 229 negative cases the GPs reported a retinopathy: specificity 84%. Of the 11 missed cases, 7 had stage I retinopathy and four showed more serious abnormalities (hard and soft exudates, macular oedema) Further training of GPs in the art of ophthalmoscopy is recommended.