We have investigated the migration patterns of normal LEW rat splenic lymphocytes (SLs) radiolabeled in vitro with [2-3H]adenosine and adoptively transferred i.v. into LEW hosts bearing LBNF1 heterotopic cardiac allografts. Twenty-four hours after cell transfer, the animals were killed and the radioactivity of all lymphoid and nonlymphoid tissues measured in a beta counter. The following experimental groups were studied: group 1, untreated recipients acutely rejecting their grafts at 7 days after transplantation; group 2, actively and passively enhanced recipients bearing long-term surviving grafts, at 7, 14 to 18, and 25 days; group 3, cyclosporin A-treated recipients; and group 4, B rats, each bearing indefinitely surviving grafts, at 7 and 20 to 30 days. In group 1, 28% of recoverable activity was found in spleen and 22% in mesenteric and peripheral lymph nodes. In animals with well functioning grafts of groups 2 and 3, SLs accumulated in both organs equally (25 to 27%). In animals in group 4, SLs migrated primarily to lymph nodes (30%) and away from spleen (20%). Sequestration in nonlymphoid tissues of animals experiencing graft rejection was higher than those with prolonged or indefinitely surviving hearts. By using mouse anti-rat monoclonal antibodies, the quantitative relationship between T cell subpopulations in transferred cell suspensions and in lymphoid organs of grafted hosts was also assessed. Lymphocyte migration patterns are influenced dramatically by the immunological status of recipients of vascularized organ allografts.