NIDDM patients have a two- to fourfold increased risk of CHD relative to nondiabetic subjects. This excess risk is explained only partially by increased levels of standard risk factors. We compared the plasma concentrations of Lp(a) in NIDDM patients (n = 260) and nondiabetic subjects (n = 336) who participated in a population-based study (San Antonio Heart Study). Lp(a) was measured using a monoclonal anti-Lp(a) antibody. NIDDM patients and nondiabetic subjects had similar Lp(a) concentrations for both men (13.6 +/- 1.5 vs. 16.1 +/- 1.4 mg/dl) and women (12.6 +/- 0.8 vs. 15.9 +/- 1.3 mg/dl) (P = 0.361). Duration of diabetes and level of fasting glycemia were not significantly related to Lp(a) concentrations. Lp(a) levels were significantly higher in patients who had higher total and LDL cholesterol levels. We conclude that in a large population-based study, Lp(a) levels are not increased in NIDDM patients.