A number of samples of mayonnaise were examined for added gums by first the precipitation of the protein with trichloroacetic acid and then the alcohol precipitation of water-soluble “gum.” Although the hydrolyzed precipitate gave a positive copper reduction and Molisch test, positive identification of gum could not be made. The IR spectrum confirmed the fact that the false positive for gums was due to the presence of mustard flour in the mayonnaise.