Lung tissue specimens, obtained during lung biopsy or resection, were morphologically and immunohistochemically studied in 27 patients with Langerhans cell (LC) histiocytosis (LCH). The latter was diagnosed on the basis of the expression of CD1a and S-100. Without immunophenotyping, its diagnosis was difficult due to impaired tissue architectonics (sclerosis, bullous transformation) and artifacts that were inevitably present during lung biopsy. LCs in the infiltrates were shown to be capable for apoptosis. Induction of LC apoptosis may be regarded as a therapeutic strategy.