We observed in our in vitro studies that human leukocytes were attached by their complement receptors to the basement membrane zone (BMZ) of the skin specimens pretreated with pemphigoid antibodies and complement. The resultant histologic feature was very similar to that of an early stage of the inflammatory reactions observable in the lesions of bullous pemphigoid. Eosinophils were also attracted to the BMZ in proportion to their number in cell suspensions, but the adhesion of eosinophils occurred neither selectively nor excessively. The nitroblue tetrazolium (NBT) test, which was carried out after the leukocyte attachment test, demonstrated that only those leukocytes bound specifically to the BMZ incorporated NBT dye complexes vigorously to form formazan crystals in their cytoplasms. The present studies showed that complement-fixing anti-BMZ antibodies induce enhancement of leukocyte activities as well as immune adherence to the BMZ, indicating that the enhanced leukocyte function plays a role in the separation between epidermis and dermis in bullous pemphigoid.