Using an immunoelectron microscopic technique we have compared the ultrastructural localization of IgG and complement (C3) in the basement membrane zone of three typical cases of bullous pemphigoid and three atypical variant cases (nodular, polymorphic and localized pemphigoid, respectively). There was no significant difference in the in vivo ultrastructural localization of these immunoreactants between the typical and the atypical cases of pemphigoid. In all cases IgG and C3 were detected between the basilar surface of the basal keratinocytes and the basal lamina. Moreover, the in vitro binding sites of circulating anti-basement membrane zone antibodies were identical in the case of nodular pemphigoid and a typical pemphigoid as control. We also observed that immunoreactants were not deposited beneath melanocytes.