Iterative hemodialysis causes only exceptionally anaphylactic reactions. In those cases it has been possible to incriminate sterilizing agents (ethylene oxide, formaldehyde) and in a few cases the membrane. We report the case of one patient suffering from a chronic renal failure who had been undergoing hemodialysis treatment for more than six years in whom we noticed anaphylactic reactions at the beginning of each dialysis session carried on with cuprophan. We were able to use three different types of dialysis membranes: cuprophan, polyacrylonitrile and cellulose acetate, and two means of sterilization: ethylene oxide and gamma rays. The disorders we observed do not seem to be related to the phenomena usually observed during hemodialysis. The clinical signs linked with hypereosinophilia (13,000/mm3), hyperbasophilia (140/mm3) and an increase in total serum IgE disappeared when cuprophan membrane was replaced by cellulose acetate. One year later, hypereosinophilia had disappeared, hyperbasophilia had subsided, total IgE remained high. We conclude that IgE dependent anaphylaxis might be due to one component of the cuprophan membrane.