In vivo leukocyte recruitment was monitored upon superfusion of the exposed mouse cremaster with fMLP. (A) Emigration was determined from the total number of cells observed in the extravascular space adjacent to the observed venule within the microscopic field of view (FOV). (B) Rolling flux was measured as the number of rolling leukocytes that pass through a 100-µm section of vessel per minute. (C) Rolling velocity was calculated from the time required for a cell to roll along a 100-µm length of vessel and is expressed as micrometers per second. (D) Cell accumulation was quantified as the number of adherent cells within a 100-µm length of venule in 5 min. A cell was deemed adherent if it remained stationary for at least 30 s. (E) The percentage of crawling cells was determined from the number of adherent cells that showed a clear crawling behavior. Data are presented as mean ± SD values from three GEF-H1^+/+ and three GEF-H1^−/− mice. ANOVA with Bonferroni's correction was performed to determine p-values (ns, not significant; *, P < 0.05; **, P < 0.001).