In five patients who have experienced anaphylaxis and in 29 patients who have not had such episodes during hemodialysis, we have performed two immunologic studies: cutaneous testing with ethylene oxide-human serum albumin (ETO-HSA) and ELISA for IgE against ETO-HSA. Four of five patients with reactions had positive cutaneous tests, whereas only one nonreactor had a positive skin test (p less than 0.0002). The same four of five patients with reactions also had positive ELISA results, whereas three nonreactors has positive ELISA results (p less than 0.003). In this group of patients, the positive predictive value of cutaneous testing (80%) is somewhat higher than that of ELISA testing (57%). However, the sensitivity, specificity, and negative predictive values are similar. We conclude that cutaneous testing with ETO-HSA probably offers a small advantage over IgE against ETO-HSA as determined by ELISA.