To determine the effect of hydrochlorothiazide on total cholesterol, baseline total cholesterol and blood pressure were determined in 618 hypertensive subjects in a hypertension clinic in Pusan, Korea. After 12-24 months (mean follow-up time 14 months), total cholesterol and blood pressure measurements were repeated. In the group whose therapy included hydrochlorothiazide (n=436), total cholesterol fell by 8+/-39 mg/dL. Those not treated with a diuretic (n=182) had an identical fall in total cholesterol of 8+/-42 mg/dL (P < 0.001 for change from baseline). Patients with a baseline total cholesterol >200 mg/dL were asked to reduce intake of saturated fat. Change in total cholesterol for 180 patients on this diet and hydrochlorothiazide was -24+/-31 mg/dL (P < 0.0001); for 71 patients on the diet and non-diuretic therapy, change was -22+/-35 mg/dL (P < 0.0001). There was no change in total cholesterol in either drug group for those with a baseline value less than or equal to 200 mg/dL.