Markedly increased plasma lipoprotein(a) [Lp(a)] levels have recently been reported in continuous ambulatory peritoneal dialysis (CAPD) patients but the genesis is obscure. Lp(a) levels in CAPD are in general higher than in hemodialysis (HD) patients, suggesting that the dialysis procedure might be of importance. In the present study, we investigated relationships between Lp(a) and parameters related to the dialysis procedure per se (dialysis dose, peritoneal glucose absorption, protein losses and protein clearances) in 32 adult CAPD patients. Uremic patients treated with HD (n = 73) as well as a group of 43 healthy subjects served as control groups. The plasma level of Lp(a) was significantly higher in the CAPD patients (median 28.2 mg/dl) than in the HD patients (median 9.2 mg/dl) and the healthy controls (median 7.0 mg/dl), whereas Lp(a) levels in the HD patients did not differ from the healthy controls. In the CAPD patients, significant correlations were found between Lp(a) and 24-hour peritoneal and total clearance for albumin (r = 0.472 and r = 0.368, p < 0.01 and p < 0.05, respectively), and between Lp(a) and 24-hour peritoneal clearance for beta(2)-microglobulin (r = 0.421; p < 0.05). Similar correlations were found between Lp(a) and 24-hour peritoneal albumin excretion, total albumin excretion and peritoneal beta(2)-microglobulin excretion. Furthermore, a significant correlation was found between Lp(a) and peritoneal glucose absorption (r = 0.352; p < 0.05). Serum cholesterol showed significant correlations with 24-hour .peritoneal albumin loss and 24-hour peritoneal beta(2)-microglobulin clearance, whereas LDL cholesterol showed a significant correlation with 24-hour peritoneal beta(2)-microglobulin clearance. In a longitudinal study of 12 CAPD patients, Lp(a) levels increased significantly between the start of CAPD and at follow-up 3-5 months later. The correlation of the markedly increased levels of Lp(a) with peritoneal albumin and beta(2)-microglobulin clearance suggests that the mechanism behind the increased Lp(a) levels may be related to the large protein losses in CAPD, perhaps via an increased synthesis rate of apolipoprotein (a) in the liver or via decreased Lp(a) catabolism in CAPD patients. Finally, the correlation between Lp(a) and peritoneal glucose absorption also indicates that the increased plasma Lp(a) levels in CAPD are related to the dialysis procedure, in particular peritoneal transport of proteins and glucose.