A double-blind study was carried out in 64 Type II diabetic patients, controlled with diet therapy and sulphonylureas (glibenclamide or chlorpropamide), who had associated hyperlipoproteinaemia which could not be normalized during a run-in period of 2 months by hygiene and dietary measures alone. The patients were allocated at random into 4 groups and each group was treated over 4 months with bezafibrate (600 mg/day) or fenofibrate (300 mg/day) in addition to their glibenclamide (5 to 15 mg/day) or chlorpropamide (250 to 500 mg/day) therapy plus diet. The results of monthly laboratory investigations showed that both hypolipaemic agents produced significant reductions in serum triglycerides, total cholesterol and LDL cholesterol and an increase in HDL cholesterol. There was a significantly greater increase in HDL cholesterol in patients treated with bezafibrate and glibenclamide, particularly in women, and greater control of blood glucose in those on bezafibrate. Both hypolipaemic drugs were well tolerated. Slight increases were recorded in serum transaminases in fenofibrate patients and in bleeding time in bezafibrate patients. It is concluded that, because of its greater effect on blood glucose and HDL cholesterol, the combination of bezafibrate with glibenclamide would appear to be the best of the regimens studied for the treatment of non-insulin-dependent diabetics with associated hyperlipoproteinaemia.