We report the results of mAb inhibition studies of human lymphocyte-high endothelial venule interaction in vitro. These studies in which T cells from both normal donors and from a LFA-1-deficient patient were used indicate that in addition to a system of organ-specific 90-kDa "homing" receptors on lymphocytes, LFA-1 is also involved in lymphocyte recirculation and homing.