Sera of patients with paraneoplastic pemphigus (PNP) characteristically immunoprecipitate five proteins, observations confirmed with the sera examined in this study. The proteins characterized thus far as autoantigens in PNP all belong to the plakin family of proteins and include desmoplakin, the 230 kDa bullous pemphigoid antigen, and envoplakin. The pattern of bands precipitated from metabolically labeled human keratinocyte extracts by each PNP serum was different, suggesting varying titers of antibodies against unique epitopes in various plakin family members. To further characterize this PNP antibody response, we produced fusion proteins of the homologous tail region of five plakin family members, including the recently cloned periplakin. Immunoblotting of equal amounts of each plakin tail-glutathione S-transferase fusion protein with PNP sera revealed a strong reaction with the envoplakin tail domain. Each sera also recognized periplakin, and certain sera recognized desmoplakin and plectin, and, weakly, bullous pemphigoid antigen 1. PNP sera were affinity purified with periplakin and envoplakin tail fusion proteins. Immunoprecipitation and immunoblotting with these affinity purified antibodies revealed shared as well as unique epitopes in the tail domains of these plakins. This study indicates that a homologous region in the carboxy-terminus of plakins, including the newly characterized periplakin, serves as an antigenic site in PNP.