The objective of this study was to systematically examine the role of L-selectin in leukocyte recruitment under baseline conditions and during allergic inflammation. A Type I hypersensitivity response was elicited in wild type (C57BI/6) and L-selectin-deficient mice by systemic (ip) sensitization and intrascrotal challenge with chicken ovalbumin. The cremasteric microcirculation was observed (intravital microscopy) in untreated animals (baseline), and at 4, 8 and 24 hrs post-antigen challenge in sensitized animals. Administration of an anti-L-selectin antibody, or deletion of L-selectin (L-selectin-deficient) had absolutely no affect on baseline leukocyte recruitment. Antigen challenge in wild type animals induced a significant increase in leukocyte rolling, adhesion and emigration at all time points examined. An anti-L-selectin antibody reduced antigen-induced leukocyte rolling by 60-70% at 4, 8 and 24 hrs post challenge. In addition, antigen-induced leukocyte rolling was reduced by 70% in L-selectin-deficient animals. Despite a reduction in rolling, however, antigen-induced leukocyte adhesion and emigration were not affected by either an anti-L-selectin antibody or L-selectin deletion. In conclusion, L-selectin does not play a role in leukocyte recruitment under baseline conditions. L-selectin contributes significantly to antigen-induced leukocyte rolling, however, overall leukocyte recruitment is not compromised.