The effects of cigarette smoking, alcohol intake, and oral contraceptives on plasma cholesterol, triglyceride, high density lipoprotein cholesterol (C-HDL), and low density lipoprotein cholesterol (C-LDL) were assessed in 965 12--19-year-old school-children in the Cincinnati Lipid Research Clinic's Princeton school survey. After pair matching for age, sex, race, and total plasma cholesterol, adolescent children who smoked had mean C-HDL 6.1 mg/dl lower, and mean C-LDL 4.1 mg/dl higher, than nonsmokers (p less than 0.01). These findings for C-HDL were replicated by covariance analysis, adjusting for age, race, sex, alcohol intake, and triglyceride levels. Adolescents who drank alcohol had higher C-HDL and triglyceride levels and lower C-LDL than nondrinkers, but the differences were not significant. Adolescent females taking oral contraceptives had higher triglyceride, C-HDL, and C-LDL levels than matched controls, but the differences were not significant. If a portion of smoking's contribution to coronary heart disease risk is mediated through its inverse association with C-HDL, and if smoking habits initiated in adolescence continue into adulthood, this report provides additional physiologic data relevant to programs designed to prevent, reduce, or stop cigarette smoking in the adolescent years.