Patients undergoing maintenance hemodialysis therapy have increased mortality due to cardiovascular disease. One possible etiologic factor for this increased mortality are the lipid abnormalities associated with chronic renal failure. In this study the effects of low molecular weight heparin (LMWH) and conventional unfractioned heparin (UFH) on plasma lipids were investigated in hemodialysis patients. In a group of 10 patients who had been on chronic hemodialysis for longer than 20 months, UFH was replaced by LMWH for 6 months. Baseline values of lipoprotein profile prior to the intervention were compared with results obtained after 6 months of LMWH. Control values were obtained 6 months after switching back to conventional heparin. During the LMWH treatment total cholesterol, LDL-cholesterol and triglyceride levels decreased significantly. This coincided with a significant increase in HDL-cholesterol. After switching back again to conventional heparin, the lipoprotein parameters returned to starting values. We conclude that the long-term use of LMWH instead of conventional heparin for anticoagulation during dialysis may contribute to a reduction of the cardiovascular risk factor of hemodialysis patients.