The transfer of cutaneous hypersensitivity was performed in humans, monkeys, and dogs, using the Prausnitz-Küstner (PK) reaction. Quantitative endpoint titrations were used to study reactions resulting from sera from allergic humans, monkeys, and canines. IgE antibody from dogs sensitized human and rhesus monkey skin. IgE antibody from humans and rhesus monkeys did not sensitize canine skin. The Fc receptors on primate mast cells must have broader stoichiometric adaptation for IgE Fc receptors than the analogous Fc receptors on canine mast cells.