L-selectin, one of the selectin (LECAM) members, is thought to be the lymphocyte homing receptor that mediates binding of lymphocytes to high endothelial venules of peripheral lymph nodes. Although L-selectin is probably the most well-characterized lymphocyte adhesion molecule, there are still a number of unresolved issues, one of which is exact operating mechanism in the lymphocyte-HE cell interaction. This molecule is expressed not only by lymphocytes but also by all other types of leukocytes which in fact never recirculate in the body. We have cloned cDNA encoding rat L-selectin and produced a soluble fusion protein of rat L-selectin and human IgG, and used it to identify ligand structures recognized by L-selectin, and also to produce blocking as well as non-blocking monoclonal antibodies to rat L-selectin. By using these tools, we investigated the biological significance of interaction between L-selectin and its ligand. Summary of these results are presented herein.