Multiple receptor systems mediate a variety of leukocyte adhesion capa bilities. For example, the T cell receptor is utilized for specific adhesion of T lymphocytes to cells bearing foreign antigen plus MHC (I), and other cell-cell interaction molecules such as CD2 and LFA-3 augment these antigen-specific interactions (2). To facilitate tissue-specific migration and recirculation of lymphocytes through lymphoid organs, at least two dis tinct proteins, MEL-14 (3) and gp90/CD44 (4), have evolved to function as homing receptors, and additional leukocyte cell-cell interactions are carried out by the LeuCAM molecules in the [32 integrin family (5). In addition to cell-cell interactions, interest is growing in the means by which extracellular matrix (ECM) influences leukocyte differentiation, tissue localization, and inflammatory functions. This review will focus mainly on the emerging roles for PI integrins (VLA proteins) as adhesion receptors for ECM and as cell-cell adhesion receptors. Although I do not emphasize other established cell-cell adhesion systems, involving T cell receptors, homing receptors and P2 integrins, fascinating examples have emerged of functional synergy and overlap