In an immunoblot analysis with human epidermal extract as a source of antigens, all (28/28) pemphigus vulgaris (Pv) sera showed a specific reactivity with a 130-kD protein. Several, but not all, Pv sera reacted with similar antigens in both a bovine muzzle desmosome preparation and extract of cultured human squamous carcinoma cells. On the other hand, some pemphigus foliaceus (Pf) sera exhibited reactivity with a 150-kD protein, which is most likely desmoglein I, in both the human epidermal extract and the bovine desmosome preparation, but no Pf serum reacted with this antigen in the squamous carcinoma cell extract. Furthermore, 4/16 Pv sera also reacted with a 150-kD protein in the desmosome preparation, which seemed to be the same as Pf antigen. These results show a relationship between antigens of both Pf and Pv and desmosomes, as well as heterogeneities of both Pv and Pf antigens in terms of antigenic molecules or epitopes. Furthermore, this study presents the possibility that immunoblot analysis can be routinely used for differentiation of Pv and Pf antibodies.