In a majority of patients with anaphylaxis to dialysis, ethylene oxide has been identified as an etiologic agent. In a significant minority of patients sustaining such reactions, the antigen remains unidentified. Conflicting results have been published with regard to isocyanates as a possible antigen. The authors studied 19 hemodialysis patients with anaphylaxis in whom IgE against ethylene oxide-human serum albumin (ETO-HSA) was not identified (Group 1) and 25 peritoneal dialysis patients without anaphylaxis (Group 2). IgE against toluene diisocyanate-human serum albumin (TDI-HSA) was found in one patient in Group 1, and a similar incidence of IgG against TDI-HSA in Group 1 (16%) and Group 2 (12%) was noted. The results do not suggest that IgE against TDI-HSA is an important cause of dialysis anaphylaxis.