Paraneoplastic pemphigus (PNP) is an acquired autoimmune disorder characterized by severe mucosal erosion, and polymorphous cutaneous lesions associated with neoplasia. PNP patients have circulating autoantibodies that bind to stratified and nonstratified epithelia. Previously, we showed that envoplakin was a component of the antigen complex recognized by PNP sera. In the present study we generated a monoclonal antibody, EVP-YS, against human envoplakin. The antibody bound to keratinocyte cell surfaces and reacted with the 210-kDa PNP antigen, confirming its specificity for envoplakin. The variable regions of the heavy (H) and light (L) chain genes were cloned from the hybridoma and shown to belong to mouse H chain subgroup III and kappa light chain subgroup V, respectively. The L chain of EVP-YS was 98% identical to the k chains of some autoantibodies and anti-nucleic acid antibodies, and had an identical amino acid sequence in all three complementary determining regions, suggesting that the H chains determine the specificity of the EVP-YS-envoplakin interaction. The EVP-YS antibody can be used to evaluate the sensitivity and specificity of clinical, histological, and immunological criteria for diagnosing PNP.