Although low-molecular-weight heparin (LMWH) has been reported to lower serum triglycerides and raise HDL in patients previously receiving classic heparin for hemodialysis by sparing lipoprotein lipase activation, this is not universally accepted. To evaluate this effect we studied 14 hypertriglyceridemic patients on hemodialysis for a median of 61 months (range 6-168 months); six were males and eight females, with a median age of 54 years (range 30-78). Eight patients were on bicarbonate and six on acetate HD. Eight were receiving EPO. All had been given conventional heparin, 102 +/- 5.8 IU/kg, at least for the last six months (control period) before switching to LMWH. Mean LMWH dose was 77 +/- 3.1 IU/kg. Fasting levels of total cholesterol (TC), triglycerides (TG) and HDL were measured monthly during the control period and every trimester for the next 36 months. Serum lipoproteins were measured at months 0 and 36 of the trial. TC, Lp alpha and beta showed no significant change. Serum TG and Lp pre-beta dropped significantly, to almost normal levels. EPO treatment, serum iPTH levels or dialysate buffer did not seem to influence this effect. HDL rose significantly higher in women than in men. It is concluded that LMWH substantially lowered the abnormally high serum TG and Lp pre-beta to almost normal and raised serum HDL in chronic hemodialysis patients.