Five renal transplant recipients exhibited giant systemic lymphadenopathy shortly after transplantation. Biopsy specimens did not show Hodgkin's lymphoma. Immunosuppression was continued in all patients. In contrast to the rapidly fatal course of malignant lymphoma in transplant recipients, adenopathy in these five patients has uniformly resolved. Patients have been observed for 6 to 15 months with no evidence of residual disease. Interval biopsy specimens are not malignant. Each patient received antithymocyte globulin from a single lot for 10 to 21 days after transplantation. During administration, T cell lymphocytes were suppressed to 5% of control values. When lymphadenopathy occurred, T cell values rebounded to 371% of control values. Toxoplasmosis titers as well as viral cultures of lymph node biopsy specimens were negative. These data indicate a benign course of this histologically malignant disease and suggest a lymphoblastic rebound phenomenon to antithymocyte globulin.