A Japanese woman with lichen planus pemphigoides is reported. Immunologic characteristics of lichen planus pemphigoides antigen in the patient were investigated by indirect immunofluorescence and compared with those of bullous pemphigoid antigen or epidermolysis bullosa acquisita antigen. Ultrastructural localization of lichen planus pemphigoides antigen was studied with the use of immunoelectron microscopic techniques. Lichen planus pemphigoides antigen showed localization similar to that of bullous pemphigoid an tigen but different from that of epidermolysis bullosa acquisita antigen. The antigenic stability of lichen planus pemphigoides antigen was different from that of bullous pemphigoid antigen or epidermolysis bullosa acquisita antigen. Thus this study demonstrates that lichen planus pemphigoides antigen is different from bullous pemphigoid antigen. © 1990, American Academy of Dermatology Inc.. All rights reserved.