After surgical trauma, leukocyte rolling is initially normal in L-selectin-deficient mice and reduced at later times, whereas leukocyte rolling is initially absent in P-selectin-deficient mice but induced later. Here, we examined the possibility that P- and L-selectin support rolling at different characteristic velocities using intravital microscopy of venules of the exteriorized cremaster muscle venules of wild type (WT) and P- and L-selectin-deficient mice. At > 50 min after exteriorization, rolling in P-selectin-deficient mice occurred at significantly higher velocities (129 +/- 89 microns/s) than in WT mice (49 +/- 23 microns/s). Rolling velocity distribution in L-selectin-deficient mice was similar to WT mice immediately after exteriorization. Histological examination of Giemsa-stained whole-mount preparations in cremaster muscle venules revealed that the majority of rolling cells (approximately 90% in all genotypes) were granulocytes. We conclude that P-selectin mediates leukocyte rolling at velocities < 50 microns/s, whereas L-selectin sustains more rapid rolling. Under physiological conditions, P- and L-selectin synergize to support rolling at velocities between 20 and 70 microns/s as seen in WT mice.