Blindness in diabetics is largely due to retinopathy and/or cataract. Hyperglycaemia and the duration of diabetes are major risk factors for the development of cataract and retinopathy. This review details some of the reactions of glucose that are relevant to the development of complications, and follows the elucidation of monosaccharide autoxidation and its relevance to the aldose reductase reaction and its determination. Inhibitors of this 'aldose reductase' reaction are shown to have a number of effects which may be of importance to their action in vivo. The pharmacological implications of chemotherapy for diabetics with complications are briefly discussed.