From the 10 North American study populations of the Lipid Research Clinics Program, mean levels of plasma high-density (HDL) cholesterol were contrasted between users of eight categories of prescribed medications and a control group of nonusers of those categories matched for age, sex, study population and ponderosity. Women taking propranolol had a mean HDL cholesterol level 12 mg/dl lower than nonusers (p < 0.05). Men taking phenytoin had a mean HDL cholesterol level more than 18 mg/dl higher than nonusers (p < 0.05). Men taking benzodiazepine derivatives had a mean HDL cholesterol level 3.3 mg/dl lower than nonusers (p < 0.05). No significant differences were found between users and nonusers of thiazide diuretics, chlorthalidone, barbiturates, sympathomimetics or antihistamines.