A 57-year-old woman was admitted because of severe bradycardia and hypotension caused by an anti-arrhythmic agent and beta-blocker. For 19 months before admission, she had been undergoing hemodialysis with an F8-HPS polysulfone membrane hemodialyzer without any complications. In 2 dialysis sessions after admission, when a BS polysulfone membrane was used, she experienced anaphylactoid shock with severe hypotension leading to syncope, dyspnea and vomiting, just after the start of hemodialysis. After the anaphylactoid shock, her dialyzer membrane was changed to a cellulose triacetate membrane and she did not suffer from such attacks. This case indicates that severe anaphylactoid shock may be caused by a biocompatible dialyzer membrane and that the reactions of patients to each polysulfone membrane may differ among polysulfone membranes made by different manufacturers.