The integrins are a family of transmembrane glycoproteins that serve as cell-cell and cell-substratum adhesion molecules and help regulate cellular morphology, differentiation, and proliferation. The integrin repertoire of a cell may therefore influence its behavior under resting conditions or following malignant transformation. For this reason, the distribution of integrins in normal lung tissues was determined using monoclonal antibodies against integrins of the beta 1 (VLA) and beta 3 (cytoadhesin) subfamilies and compared with the distribution in a limited number of lung carcinomas. The integrin subunits that bind to collagen and laminin (alpha 1, alpha 2, alpha 3, and alpha 6) and the alpha subunit, which can pair with beta 1, beta 3, or beta 5 and promote fibronectin, fibrinogen, or vitronectin binding, were the predominant integrins expressed on the major cell types of the lung, i.e., bronchial epithelium, vascular endothelium, and smooth muscle. Strong expression of the alpha 5 beta 1 fibronectin receptor and the beta 3 subunit was restricted to the endothelium of large vessels. Integrin expression by the lung carcinoma cells was somewhat heterogeneous; however, the tumors tended to express fewer integrins than did the normal bronchial epithelium.