Intraepithelial lesions comparable to those which characterize pemphigus vulgaris developed following repeated intramucosal injections of monkey lip with pemphigus antibodies. Transfer experiments were performed, injecting samples of patients’ sera or their IgG fractions, once, twice, or three times into mucosal locations. At sites injected with pemphigus antibodies, immunofluorescence studies almost invariably revealed their binding to the intercellular region of the mucosal epithelium. Suprabasal clefts could be detected in 6 of 16 sites which had received three injections; five of these occurred 21–25 h after the first of three injections. Controls utilizing sera of patients with bullous pemphigoid, systemic lupus erythematosus, normal human serum and normal human IgG were all negative.