Contact with members of the plant family Commelinaceae, which includes wandering jew (Commelina spp. formerly called Tradescantia spp.) and inch plant (Callisia fragrans), can cause cell-mediated contact dermatitis in dogs. However, reports of canine IgE-mediated hypersensitivity to these plants have not been published. The purpose of this study was to discover whether IgE antibodies specific for extractable components of C. fragrans could be identified in serum from a dog that had anaphylactic shock after exposure to the plant and after skin patch testing with the sap from a leaf of C. fragrans. Separate aqueous extracts of leaves and flowers of C. fragrans were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Serum from a dog with no history or symptoms of any allergies showed no specific IgE antibodies against the leaf extract. Serum from a dog with clinical symptoms of delayed, but not immediate hypersensitivity to leaf sap from C. fragrans, showed only minor IgE recognition of a single 65 k component in sap extracted from leaves harvested in summer but not in winter. However, IgE antibodies to a serum dilution of 1:200 specific for several components of the leaf extract were seen in serum from the dog that had anaphylactic shock after exposure to sap. The molecular weights of these molecules were in the range 51 k to 83 k. The bands on the immunoblots did not match with prominently stained protein bands in the gel, but instead identified molecules in a lightly stained area of the gel with diffuse bands. Testing for glycans indicated that the carbohydrate side chains of glycoproteins contributed significantly to the immunoreactivity of the putative allergens. All three dog sera failed to show any immunoreactivity against the extract from the flowers of C. fragrans.