The predictors of premature coronary atherosclerosis were examined in 203 patients (99 men aged less-than-or-equal-to 50 years, and 104 women aged less-than-or-equal-to 60 years) undergoing elective diagnostic coronary arteriography. Age, cigarette smoking, hypertension, obesity, diabetes, positive family history of premature coronary artery disease (CAD), and plasma levels of total cholesterol, triglyceride, lipoproteins (i.e., very low, intermediate-, low-, and high-density [HDL] lipoproteins and their subfractions [HDL2 and HDL3], and lipoprotein [a]) and apolipoproteins (apoA-1, apoA-2 and apoB, respectively) were examined using univariate analyses and multivariate logistic regression. In men, age (p < 0.05), smoking (p < 0.05), and plasma triglyceride (p < 0.02) and apoA-1 (p < 0.05) levels were independently associated with CAD. In women, smoking (p < 0.001) and plasma apoB levels (p < 0.04) were the strongest variables independently associated with CAD. It is concluded that the "nontraditional" risk factors (plasma apoA-1 and apoB levels) are better predictors of premature CAD than are plasma lipoproteins and that smoking is the strongest of the traditional nonlipid risk factors.