The Oslo Hypertension Study started in 1972 and lasted for 66 (range 60-78) months. A total of 785 healthy men, aged 40 to 49 years, with mild hypertension were randomised to a drug-treated group and to an untreated, control group. The drugs used for treatment were hydrochlorothiazide alone in 36%, hydrochlorothiazide and propranolol in 26%, hydrochlorothiazide and methyldopa in 20%, and other drugs in 18%. A total of 95% in the drug-treated group received hydrochlorothiazide. Pressure complications, such as stroke and aneurysms, only occurred in the control group. Coronary events were more numerous in the drug-treated group, so that the total incidence of cardiovascular complications did not significantly differ between the treated and untreated groups. After 5 and 10 years, total mortality was found to be the same in both groups. However, the 10-year coronary heart disease mortality was significantly higher in the drug-treated group than in the untreated controls (14 v 3, p less than 0.01). Possible reasons for the failing effect of drug treatment of hypertension on coronary heart disease is discussed, and attention is drawn to the adverse effect of diuretics and beta-adrenergic blockers, both on lipid and carbohydrate metabolism. This is in contrast to the alpha-adrenergic blocker, prazosin, which has been shown to improve the blood lipid profile.