The selectins are lectin-like cell surface glycoproteins that have been implicated in playing a crucial role in the initiation of leukocyte adhesion to endothelial cells (ECs) during inflammation. Binding of selectins under conditions of flow mediates leukocyte rolling, which in vivo is almost exclusively observed in venular microvessels. We have shown in previous experiments that intraperitoneal treatment of rabbits with interleukin-1 beta (IL-1) increases leukocyte rolling in exteriorized mesenteries. In the present study, we used immunohistochemistry of mesenteries and found that IL-1 induced a marked E-selectin immunoreactivity, preferentially in venules. We therefore hypothesized that the increased rolling in response to IL-1 may be related to the induction of E-selectin on venular ECs. Intravital microscopy was used to investigate interactions between leukocytes and ECs after intraperitoneal application of IL-1. The rabbit E-selectin monoclonal antibody (MoAb) 9H9 significantly reduced rolling of leukocytes by approximately 40%. Vehicle alone, class- matched control MoAb or the nonblocking anti-E-selectin MoAb 14G2 had no effect on rolling. These results indicate that leukocytes roll on inflamed venular ECs partly through interactions with E-selectin. Furthermore, we propose that the restricted E-selectin immunoreactivity by venular ECs contributes to the remarkable difference seen between arterioles and venules in exhibiting leukocyte rolling in vivo.