Patients with terminal renal insufficiency suffer from an increased incidence of atherosclerotic diseases. Elevated plasma concentrations of lipoprotein(a) [Lp(a)] have been established as a genetically controlled risk factor for these diseases. Variable alleles at the apo(a) gene locus determine to a large extent the Lp(a) concentration in the general population. In addition, other genetic and nongenetic factors also contribute to the plasma concentrations of Lp(a). We therefore investigated Apo(a) phenotypes and Lp(a) plasma concentrations in a large group of patients with end-stage renal disease (ESRD) and in a control group. Lp(a) concentrations were significantly elevated in ESRD patients (20.1 +/- 20.3 mg/dl) as compared with the controls (12.1 +/- 15.5 mg/dl, P < 0.001). However, no difference was found in apo(a) isoform frequency between the ESRD group and the controls. Interestingly, only patients with large size apo(a) isoforms exhibited two- to fourfold elevated levels of Lp(a), whereas the small-size isoforms had similar concentrations in ESRD patients and controls. Beside elevated Lp(a) concentrations, ESRD patients had lower levels of plasma cholesterol and apolipoprotein B. These results show that elevated Lp(a) plasma levels might significantly contribute to the risk for atherosclerotic diseases in ESRD. They further indicate that nongenetic factors related to renal insufficiency or other genes beside the apo(a) structural gene locus must be responsible for the high Lp(a) levels.