The ultrastructural localization of the pemphigus vulgaris (PV) and pemphigus foliaceus (PF) antigens in cultured human squamous carcinoma cells was observed using immunogold electron microscopy. Both the PV and PF autoantibodies bound only to the extracellular portion of the desmosomal structures. After incubation at 37 degrees C, the PV antigen-antibody complexes were observed within the cultured cells. PV and PF antigen expression was markedly reduced when the cells were cultured in medium with a low Ca2+ concentration.