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 less than 0.05), smoking (p less than 0.05), and plasma triglyceride (p less than 0.02) and apoA-1 (p less than 0.05) levels were independently associated with CAD. In women, smoking (p less than 0.001) and plasma apoB levels (p less than 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.