SUMMARY.—Case studies of 2 patients with bullous skin lesions are reported, one of whom also had thyrotoxicosis and rheumaloid arthritis, and results of serological tests for the “pemphigus” antibody in 92 patients with other immunopathies. The “pemphigus” antibody, which reacts with the intercellular substance of squamous epithelium, was demonstrable in 1 case at low titre before the onset of widespread skin lesions; titres correlated with the activity of the skin lesions of pemphigus vulgaris; and the antibody was detected at low titre in diseases other than pemphigus vulgaris, including myasthenia gravis (2 cases) and systemic lupus erythematosus (1 case). The possible clinical and serological overlap between pemphigus vulgaris, myasthenia gravis and systemic lupus erythematosus was interpreted from the standpoint of thymic dy