Subcutaneous (s.c.) inoculation of the 85-4LN subline, derived from a lymph nodal metastasis of the Epstein-Barr virus (EBV) transformed human chronic lymphocytic leukemia (CLL) B cell line, EBV-CLL (1), produced progressively growing lethal tumors in 31/35 nonirradiated (88.6%) and 22/25 (88%) of whole-body irradiated (440 rad) nude mice. In contrast, EBV-CLL(1) could produce progressive tumors only in irradiated nude mice. All 85-4LN cells had Epstein-Barr virus nuclear antigen and reacted with pan B and anti-la antibodies. The morphology and ultrastructural features was consistent with the lymphoblastoid nature of the cells. In all s.c. tumor bearing mice, there was enlargement of the spleen and draining lymph nodes. Karyological studies revealed human cells in the spleen and draining nodes in all the mice investigated. Metastases in nonlymphoid organs were seen in 1/8 irradiated and 8/12 nonirradiated mice. The subline contained 77% cells with 47,XY, +12 and 23% cells with 45,XY karyotype. The clone with trisomy 12 did not have any growth advantage either in s.c. transplants or in splenic/lymph nodal metastases. Treatment with the maximum permissible doses of methotrexate (MTX) or chlorambucil (CBL) revealed xenografts to be more sensitive to MTX than CBL. A clone with a 1g+ marker, i.e., 46,XY,Dup(1) (q11----q32) appeared to be associated with resistance to CBL. We have not seen any previous report on the growth and dissemination of human CLL B cells in nonirradiated nude mice. The 85-4LN subline, thus, provides a model for studying the progression, dissemination and therapeutic response of human CLL-B cells.