The tissue distribution and species expression of the antigens in adult linear IgA disease (LAD) and chronic bullous dermatosis of childhood (CBDC) was studied and compared with those of bullous pemphigoid (BP) and epidermolysis bullosa acquisita (EBA) antigens. Positive sera from five adult LAD patients, 15 CBDC patients, three BP patients and two EBA patients were studied, using skin and mucosal tissues of humans and animals as substrates. The tissue distribution and phylogenetic distribution of adult LAD antigen and CBDC antigen were the same, suggesting that they are identical diseases. The antigens were both demonstrable only in stratified squamous epithelia and amnion of mammalian species. They were absent from transitional and columnar epithelium. The EBA antigen was not expressed in pig tissues or human placenta, unlike adult LAD and CBDC antigens. Expression of adult LAD, CBDC and BP antigens was observed in all tissues except bladder, which lacked LAD and CBDC antigens. These results suggest that the antigens in adult LAD and CBDC are the same and differ from EP and EBA antigens.