Hyperlipidemia is one of the major risk factors for cardiovascular death in long-term hemodialysis (HD) patients. To clarify whether unfractionated heparin (UFH) contributes to the pathogenesis of hyperlipidemia, nine Type IIb, seven Type IV, and 10 normolipidemic patients, who had been dialyzed with 80.7 IU/Kg heparin, were dialyzed with 40 anti-Xa U/kg of low molecular weight heparin (LMWH) (Logiparin, Novo-Nordisk, Gentfe, Denmark) for 6 months. Seven normolipidemic patients were also dialyzed with heparin as controls. Decreases in triglyceride (TG) during HD with LMWH were significantly less than those with heparin. However, lipoprotein lipase activities (LPL) during HD with LMWH and heparin, and those before and after 6 months on LMWH, were no different. During the 6 months on LMWH, serum total cholesterol, TG, and alpha lipoprotein significantly decreased in Type IIb patients but did not change in Type IV. In contrast, beta lipoprotein slightly increased in Types IIb, IV, and normolipidemic patients who were dialyzed with LMWH but was unchanged in the controls. These observations suggest that UFH aggravates hyperlipidemia in patients, but these effects cannot be attributed to depletion of endothelial LPL liberated by UFH.