Increased leukocyte-endothelial interactions and angiogenesis are observed in the ocular vasculature of mice lacking the cell surface heparan sulfate proteoglycan syndecan-1. Here we investigate the interaction of defined leukocyte populations of syndecan-1 knockout (KO) and wild-type mice with endothelial cells in vitro. Heparin is used to substitute for the lack of syndecan-1 heparan sulfate.