Adhesion molecules are important regulators of interactions between endothelial cells and leukocytes during leukocyte migration. Limited information exists about adhesion molecules in species other than mouse and man. Thus, expression, regulation and functional aspects of E-selectin, vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1 (ICAM-1) were studied in cultured bovine aortic endothelial cells (BAEC), and in tissue from cows with mastitis or induced inflammation. Cultured BAEC were stimulated with recombinant bovine tumor necrosis factor alpha (rbTNF- a ) or lipopolysaccharide (LPS) for various periods of time and surface and/or mRNA expression was measured by flow cytometry or quantitative reverse transcriptase polymerase chain reaction (Q-RT-PCR), respectively. Tissue samples from healthy and mastitic mammary glands (MGs), and from MG tissue infused with LPS were used to study expression and regulation 'in vivo'. Function of VCAM-1 and ICAM-1 was examined using 'in vitro' binding and binding inhibition assays, with CD8+ or WC1+ T cells from blood. Surface expression of E-selectin did not correlate with mRNA expression, however mean fluorescence intensity did. Expression kinetics of E-selectin mRNA differed between LPS and rbTNF- a . Surface expression of VCAM-1 did not vary between stimuli and ' in vitro' and 'in vivo' expression kinetics were similar. ICAM-1 mRNA expression differed between stimuli but did not differ between ' in vitro' and 'in vivo' systems. E-selectin and VCAM-1 were expressed in the teat and parenchymal MG tissue from cows with ' Escherichia coli' or 'Staphylococcus aureus'-mediated mastitis but not in nonmastitic MG tissue. 'In vitro' adhesion assays indicated that WC1+ lymphocytes may use the VCAM-1/VLA-4 or ICAM-1/LFA-1 adhesion pathways more than CD8+ cells. This study indicates a role for bovine E-selectin, VCAM-1 and ICAM-1 in mediating the adhesion of leukocytes to activated endothelium 'in vitro' and 'in vivo'. Furthermore, VCAM-1 and ICAM-1 are both important in the interaction between CD8+ or WC1+ T cells and bovine endothelium. Proportions of total L-selectin+ and LFA-1+ blood mononuclear cells did not vary over the peripartum period. However, L-selectin+ lymphocyte subsets varied in blood and milk, indicating a possible role of L-selectin in the trafficking and migration of T cell subsets into milk of dairy cattle.