The lipid patterns of plasma from 6 patients on hemodialysis (HD) and 6 patients on continuous ambulatory peritoneal dialysis (CAPD) were compared and correlated to plasma toxicity as measured by the survival of human macrophages cultured in vitro. The median values for plasma triglycerides (TG), cholesterol, low density lipoprotein (LDL) cholesterol, apolipoprotein B and lipolytic activities (lipoprotein lipase and hepatic lipase) were insignificantly higher in CAPD plasma than in HD plasma. The median high density lipoprotein (HDL) cholesterol/LDL cholesterol ratio was significantly higher in HD plasma than in CAPD plasma. In both groups systemic heparinization was followed by a significant increase in free fatty acids and in plasma toxicity. The difference in plasma toxicity was insignificant. In the whole group of patients (n = 12) toxicity in post-heparin plasma was correlated to pre-heparin very low density lipoprotein (VLDL) TG, but not to LDL TG. Separately post-heparin toxicity in CAPD plasma was correlated to pre-heparin total TG, VLDL TG and post-heparin LDL TG.