Serum lipids, lipoproteins, and major apolipoproteins and their association with previous myocardial infarction were studied in patients with non-insulin-dependent diabetes mellitus (NIDDM) and nondiabetic subjects in East and West Finland in 1982-1984. NIDDM patients had higher age-adjusted serum triglyceride and apolipoprotein B levels and a higher apolipoprotein B/apolipoprotein A-I ratio, lower serum high density lipoprotein (HDL) cholesterol and apolipoprotein A-1 levels, and a lower HDL cholesterol/apolipoprotein A-1 ratio than nondiabetic subjects. With a few exceptions, these differences persisted after adjustment for body mass index, alcohol intake, physical activity, smoking, and hypertension, which suggests that the atherogenic serum lipoprotein pattern in NIDDM is an inherent feature of the disease. In general, the association of serum lipids, lipoproteins, and apolipoproteins with myocardial infarction was similar in nondiabetic subjects and NIDDM patients, although it was somewhat stronger in the diabetic subjects. A low serum HDL cholesterol/apolipoprotein A-1 ratio, which was closely linked to high serum triglyceride level, seemed to be more consistently related to myocardial infarction in NIDDM patients than in nondiabetic subjects. Serum lipids, lipoproteins, and apolipoproteins, either separately or in various combinations, could only to a small extent explain the higher prevalence of myocardial infarction in diabetic subjects compared with nondiabetic subjects when tested in multivariate analysis with other cardiovascular risk factors as background variables. The association between serum lipoproteins and myocardial infarction was largely similar in East and West Finland, two areas that differ markedly with respect to the occurrence of coronary heart disease.