Recent studies showing cross-reactivity between different pegylated compounds (4, 5), and the identification of IgE against PEG in the context of anaphylaxis (6), as well as evidence of antigen-specific inhibition of histamine release by monomeric and dimeric fractions of PEG (7), suggest that an immunoglobulin E (IgE)-mediated pathway is involved. This evidence concerns the gene IGHE and anaphylaxis.