In the present study, plasma cholesterol, triglyceride, low density lipoprotein (LDL)-cholesterol, high density lipoprotein (HDL)-cholesterol, and the major protein in LDL, apoB, were measured in 28 patients with chronic renal failure treated with hemodialysis and in 28 patients with chronic renal failure treated with chronic ambulatory peritoneal dialysis (CAPD). Elevated plasma triglycerides and reduced HDL cholesterol were frequent in both the hemodialysis and CAPD patients. However LDL levels were significantly higher in the CAPD patients as evident both by LDL cholesterol and LDL apoB. Even so, only one of the CAPD patients was hypercholesterolemic whereas 14 (or 50%) had hyperapobetalipoproteinemia (HyperapoB). Insulin-dependent diabetes was more frequent in the CAPD group but only 2 of the 9 insulin-dependent diabetics in this group had HyperapoB, and therefore, diabetes mellitus cannot account for the difference between the 2 groups. Thus HyperapoB appears to be a prevalent dyslipoproteinemia in CAPD patients and as such might be another factor which places CAPD patients at particularly increased risk of atherosclerosis.