Two patients with advanced lung cancer, histologically diagnosed as adenocarcinoma and squamous cell carcinoma, respectively, were treated with a combination of radiation and anticancer drugs (aclacinomycin-A, bleomycin, mitomycin). The lung tumors responded remarkably to this combined modality. However, the patients succumbed to pneumonia-like disease, being refractory to various antimicrobial treatments. Histologic examination revealed that the outstanding squamous metaplasia developed diffusely in the terminal bronchioles and the alveoli in all lobes of the lungs. Compared with their clinical courses and the resultant detailed pathological findings, the pathogenesis of the conditions was discussed.