To identify regions of the Desmoglein-1 (Dsg1) extracellular domain that are targeted by pemphigus antisera, cDNA sequences encoding various regions of the Dsg1 extracellular domain were ligated to sequences encoding the E-cadherin extracellular anchor and transmembrane and cytoplasmic domains. These constructs were then expressed in mammalian cells, and pemphigus sera were tested for the ability to recognize the Dsg1 extracellular domains. When analyzed by immunoblot, very few pemphigus foliaceus sera recognized the Dsg1 domains. To determine whether pemphigus sera recognize non-denatured Dsg1 domains, constructs were expressed in cultured cells and tested for reactivity with pemphigus sera using live-cell immunofluorescence. The pemphigus foliaceus sera reacted strongly with the Dsg1 extracellular domain by live-cell immunofluorescence and recognized predominantly the aminoterminal region of the Dsg1 extracellular domain. In addition, sera from patients with pemphigus vulgaris also demonstrated strong reactivity with the Dsg1 extracellular domain when tested using live-cell immunofluorescence. In contrast, sera from normal human controls and sera from bullous pemphigoid patients did not react with the Dsg1 extracellular domain. These data indicate that both pemphigus foliaceus and pemphigus vulgaris sera react with conformationally sensitive epitopes in the amino- terminal region of Dsg1.