In the Oslo study serum lipids have been studied during treatment with some of the most frequently used antihypertensive drugs. Hydrochlorothiazide induced no significant changes. However, those patients with the most marked increase in uric acid showed an increase of serum triglycerides. Total cholesterol was unchanged in these men. The beta-adrenoceptorblocking drugs propranolol, atenolol and oxprenolol caused a reduction of HDL cholesterol and an increase of total triglycerides. Total cholesterol remained unchanged. Pindolol induced no significant lipoprotein changes. Prazosin reduced total cholesterol and total triglycerides. HDL cholesterol remained unchanged. LDL + VLDL cholesterol was reduced.