Over the next few years, research can be expected to focus on the regulation of expression of the tissue-specific homing receptors, the molecular nature of the corresponding endothelial ligands, and the spectrum of factors regulating the adhesiveness of high endothelial venule cells in vivo. In addition, it would be important to elucidate whether other adhesion molecules also play a role in tissue-specific lymphocyte entry and localization into distinct regions of the lymphoid organ. The results of these studies should provide important insights into the mechanisms controlling lymphocyte trafficking into lymphoid tissues as well as chronic inflammatory sites.