Available clinical evidence indicates a high prevalence of hyperuricemia in patients with essential hypertension; this becomes accentuated with diuretic therapy. Since there is an association of hyperlipidemia with hyperuricuria and hypertension and since hyperuricemia is a feature of diuretic therapy, we explored whether these relationships might be provoked by prolonged diuretic therapy. Eighteen male patients with uncomplicated essential hypertension of mild severity were treated for 9 months with hydrochlorothiazide and supplemental potassium chloride, 100 mg and 45 mEq/day, respectively. Arterial pressure, renal function, and serum electrolyte, uric acid, blood glucose, and lipid concentrations were measured several times before and during therapy. Arterial pressure remained significantly reduced during therapy (P less than 0.001); this was associated with reduced serum potassium (P less than 0.01) and increased blood glucose and serum uric acid concentrations (P less than 0.005, P less than .025, respectively). Blood urea nitrogen, serum creatinine, sodium, cholesterol and triglyceride levels did not significantly change with treatment. Thus, although diuretics increase serum uric acid and blood glucose, their effect on serum lipid concentration is negligible.