Since heparin is an anticoagulant commonly used in hemodialysis and the patients on hemodialysis are repeatedly exposed to heparin, heparin may be the cause of the development of heparin-dependent antibodies and thrombotic complications in patients on hemodialysis. The purpose of this study was to determine the prevalence and the clinical significance of the antibodies against heparin-platelet factor 4 complexes as determined by enzyme immunoassay in patients on maintenance hemodialysis. The prevalence of anti-heparin-platelet factor 4 antibodies was higher in hemodialysis patients than in normal subjects (8.8 vs 0.0%, p<0.05). The number of past episodes of vascular access obstruction per year was significantly higher in the anti-heparin-platelet factor 4 antibody positive group than antibody negative group. Anti-heparin-platelet factor 4 antibody positive patients experienced more frequent vascular access obstructions than control subjects. In conclusion, anti-heparin-platelet factor 4 antibody might be a risk factor for vascular access obstructions in patients with end-stage renal disease on maintenance hemodialysis.