The migration of normal and malignant lymphocytes is controlled in part by selective lymphocyte recognition of high endothelial venules (HEV) at sites of lymphocyte exit from the blood. Recirculating lymphocytes appear to utilize structurally related, yet functionally distinct, 90-kD receptors to interact in an organ-specific manner with HEV in peripheral lymph nodes, in mucosa-associated lymphoid tissues (Peyer's patches, appendix), and in inflamed joint tissue (synovium). These lymphocyte "homing receptors" constitute a family of glycoprotein endothelial cell recognition elements that regulate the extravasation of circulating normal and neoplastic lymphocytes into different organs of the body, and thus play an important role in determining the characteristics of local immune responses and the patterns of dissemination of lymphoid neoplasms.