Leukocyte adhesion under flow in the microvasculature is a multistep process in which rolling adhesion is followed by firm arrest. These interactions are mediated by binding between receptors on the leukocyte surface and complementary ligands on the surface of endothelial cells. Previous work using a computational method called "adhesive dynamics" showed that the general shape of a state diagram for cell adhesive behavior in flow could be predicted by the bond reaction rates and their dependence on force. Other parameters, however, such as shear rate, particle size, and receptor and ligand density, determined the exact region of parameter space that corresponds to an adhesive behavior. In this paper, we present state diagrams for adhesion for a range of particle sizes to explain the rolling behavior for a wide range of cell diameters. Particle size is an easily controlled experimental variable, and if the locations of regions of desired adhesive behavior in the state diagram are known, then the size of particle needed to achieve a desired adhesive behavior can be predicted.