MACROPHAGES interact with other cells and components of the extracellular environment by means of adhesion receptors^1,2. Adhesion to artificial substrata in vitro facilitates isolation of macrophages³, and has been used to generate antibodies that inhibit their migration in vivo^4,5. Unlike other cell types, macrophages attach to tissue culture plastic in the absence of divalent cations. Here we use an adhesion assay exploiting this property to isolate a rat monoclonal antibody, 2F8, which totally inhibits divalent cation-independent adhesion of murine macrophages to tissue culture plastic in the presence of fetal calf serum. Immunoprecipitation from macrophages and stably transfected Chinese hamster ovary cells revealed that the antigen recognized by monoclonal 2F8 is identical to murine macrophage scavenger receptor^6,7. We propose a novel function for this molecule, previously described as an endocytic receptor, thus providing a mechanism for mononuclear phagocyte recruitment to and retention in ligand-rich tissues such as in atherosclerotic lesions.