Bronchioloalveolar carcinomas (n = 15) and other primary lung carcinomas (n = 9) were studied by PAS staining. The bronchioloalveolar carcinoma group contained three cases of carcinomas of type II pneumocytes. Cytoplasmic staining with PAS was most intense in mucus secreting carcinomas. Carcinomas of type II pneumocytes could not be differentiated from other tumors on the basis of cytoplasmic PAS staining. However, PAS positive nuclear "inclusion" were seen only in the three carcinomas of type II pneumocytes. The study indicates that PAS staining, though nonspecific, may serve as a screening test for carcinomas of type II pneumocytes by highlighting the nuclear inclusions of surfactant specific apoprotein.