High-density lipoprotein cholesterol (HDL-C), apolipoprotein (apo) A-I, and apo A-II levels were measured in 1,219 normal subjects with no clinical evidence of coronary artery disease, 81 subjects without diabetes but with "significant" coronary artery disease determined by coronary arteriography, and 151 subjects with non-insulin-dependent diabetes mellitus (48 with clinical coronary artery disease and 103 without such disease). In the normal subjects, apo A-II levels were less influenced by age, gender, and use of medications than were apo A-I or HDL-C levels. HDL-C, apo A-I, and apo A-II levels were significantly lower in subjects who had coronary artery disease with or without diabetes than in control subjects. After adjustments were made for age and sex, however, apo A-II levels were no longer significantly different between subjects with diabetes who had and those who did not have coronary artery disease. In subjects without diabetes, apo A-II may provide some advantages over apo A-I and HDL-C in the assessment of risk of coronary artery disease because it is influenced less by age, gender, and medications. In subjects with diabetes, however, apo A-II levels are similar in the presence or absence of coronary artery disease.