Inflammation in the liver and mammary glands of sheep caused by challenge infection with Taenia hydatigena or infusion of killed Staphylococcus aureus, respectively were characterized by the recruitment of both T and B cells. The patterns of migration of these two major lymphocyte subpopulations were distinctly different. While T cells seemed to migrate out of existing, flat endothelium-lined blood vessels resulting in a diffuse distribution at the sites of inflammation, B cells were characteristically present as clusters of tightly packed cells at restricted sites in the inflamed tissue. Within these B cell clusters distinct capillary vessels lined with plumb endothelial cells were always present suggesting that they were the sites of intense migration of B cells originating from the draining lymph nodes. These results indicate differential regulation of adhesion molecules on B and T cells and/or their ligands on endothelium during acute inflammatory reactions.