Abstract In vivo dynamics of the interaction between leukocytes and the endothelium following direct activation of the white blood cells (WBCs), apart from possible endothelial cell activation, were studied in arterioles, capillaries, and venules of splanchnic tissue (rabbit omentum). WBCs were isolated using either density gradient or centrifugation techniques, labeled with fluorescent dyes, and exposed to physiological solutions with or without the chemoactivator N-formyl-methionyl-leucyl-phenlyalanine (FMLP). WBCs isolated using standard density gradient separation techniques rapidly disappeared from the circulating pool following a bolus injection and were sequestered in lung microvessels. The centrifugation technique produced cells that circulated for at least 60 min. WBCs directly activated with FMLP adhered to venular endothelium but not to arteriolar endothelium, suggesting that differences in hydrodynamics in the arteriolar and venular network or fundamental differences between arteriolar and venular endothelia may explain the lack of leukocyte-endothelium adhesion (LEA) in arterioles. WBCs pretreated with FMLP had significantly longer attachment times than nontreated cells, 13.4 and 2.5 sec respectively, which may be indicative of specific receptor chemistry. Similarities in the LEA attachment-detachment process for splanchnic tissue with that previously reported for lymphoid tissue suggest that a fundamental process of cell to cell interaction may exist in all tissues.