Previously we reported a case of subepidermal blistering disease, which resembled bullous pemphigoid clinically. An immunoblot analysis revealed that the patient’s serum reacted exclusively with a 450-kD epidermal polypeptide. The 450-kD antigen was also expressed in human keratinocytes and a human squamous carcinoma (HO 1-u-1 or A431) cell line. Using the patient’s serum, cDNA clones in a bacteriophage λgt11 library derived from human foreskin keratinocytes were immune-screened. One positive clone was isolated from 2 million clones. Northern blot analysis showed that the inserted part of this clone hybridized with a more than 12-kb mRNA species derived from HO 1-u-1 cells. The deduced amino acid sequence had no homology with any other human compo