Expression of facilitative glucose transporter (Glut) isoforms was studied immunohistochemically in lung carcinomas. Glut-1 was expressed in 45 (74%) of 61 lung carcinomas, including 19 (100%) of 19 squamous cell carcinomas. No Glut-1 staining was seen in normal lung epithelium surrounding the tumors. In squamous cell carcinomas and small cell carcinomas, Glut-1 immunostaining was stronger in the central area of tumor cell nests corresponding to the hypoperfused region. Focal staining was seen in 14 (58%) of 24 adenocarcinomas, and positive staining was correlated to lesser differentiation, larger tumor size, and positive lymph node metastasis. Glut-2 was detected in normal airway epithelium, but no positive staining was seen in lung carcinomas. Glut-3 and Glut-4 were not positively stained in normal lung epithelia, but a few lung carcinoma samples showed positive reaction (9 of 61 in Glut-3; 4 of 61 in Glut-4). Glut-4 immunoexpression was seen in regenerating alveolar and bronchiolar epithelia around and in cancer tissues. Glut-5 expression was not detected in normal and tumor tissues. Reverse transcriptase-polymerase chain reaction for Glut-1, Glut-3, and Glut-4 confirmed the expression revealed by immunohistochemical analysis. Overexpression of Glut could enhance uptake of glucose into lung carcinoma cells, and the increased glucose influx could be involved in cell biologic activities.