Lipoprotein(a) (Lp(a)) serum concentrations and apoprotein(a) isoforms were measured in 64 uraemic patients treated with continuous ambulatory peritoneal dialysis (CAPD) and compared with those in 155 normal controls. The mean Lp(a) values were 44 +/- 5 mg/dl (median 30 mg/dl) in CAPD patients and 22 +/- 3 mg/dl (9 mg/dl) in controls (P < 0.01). Within the most common apo(a) isoform classes, higher concentrations of Lp(a) were seen in the CAPD patients compared with the controls (P < 0.05). These results were not influenced by differences in the frequency distribution of the apo(a) isoforms. Twenty-six CAPD patients (41%) were suffering from coronary artery disease and 63% of these patients exhibited low-molecular-weight isoforms < or = S2, compared with 31% of the patients without coronary artery disease. Furthermore a positive correlation between the daily protein (r = 0.4, P = 0.02) and albumin loss (r = 0.39, P = 0.2) into the dialysis fluid and the Lp(a) serum concentration was also observed. Therefore we suggest that the elevated Lp(a) concentrations in CAPD patients are influenced by the amount of protein loss into the dialysate and by the allelic variation of the apo(a) isoform. In addition to the typical dyslipidaemia found in CAPD patients, high levels of Lp(a) and specific isoform patterns may in turn contribute to the elevated risk of coronary artery disease and other cardiovascular complications.