To elucidate the role of epidermal growth factor (EGF) in the maintenance and repair of airway epithelial cells in adult humans, we investigated immunohistochemically whether EGF receptor (EGFR) is expressed in these cells. In the present study, we employed the AMeX method (Sato et al., 1986) for tissue preparation. We first examined the expression of EGFR in peripheral lung tissue and bronchial tissue obtained at surgery from thirteen adult patients with lung carcinoma. The results showed that there was no positive staining for EGFR in the bronchial surface epithelium, bronchial glandular cells, bronchiolar epithelium or alveolar lining cells. There was also no expression of EGFR in cells comprising areas of basal cell hyperplasia and epidermoid metaplasia in the bronchus, or alveolar cell hyperplasia and columnar cell metaplasia in fibrotic lung tissue. Second, we examined the expression of EGFR in regenerating distal airway epithelial cells, which were experimentally produced by xenotransplantation of human lung tissue into the subcutaneous tissue of nude mice. There was also no expression of EGFR at any stage of regeneration from one week through six weeks after the transplantation. It is concluded that EGFR is not expressed, at least at an immunohistochemically detectable level, by airway epithelial cells of adult humans, not only in the quiescent state but also under conditions in which epithelial cells are stimulated to replicate. Thus, it appears unlikely that the EGF/EGFR system plays an important role in either maintenance or repair of airway epithelial cells in adult humans.