The efficacy of gabexate mesilate (FOY), a synthetic serine proteinase inhibitor, was compared with that of heparin in preventing the acceleration of bleeding after hemodialysis. Transfused blood volume (TBV) was measured 24 h before and after 24 dialyses in 14 bleeding patients with impaired hemostatic function. The predialysis TBV did not differ significantly between heparin and FOY groups; however, TBV was significantly (p< .05) larger after heparin dialysis than after FOY dialysis. After dialysis, TBV was increased in eight of nine heparin patients, compared to only three of 15 FOY subjects (p< .01). FOY is an effective agent and may decrease postdialysis bleeding complications in certain high-risk patients.