Two cell lines (EH and HK) with hairy cell leukemia (HCL) immunophenotypes were recently derived from two HCL patients. Both cell lines were transplanted subcutaneously (2 x 10(5) or 2 x 10(6)/mouse) in male BALB/c nu/nu mice (n = 128) with a 97% success rate when coimplanted with nonproliferative HT-1080 fibrosarcoma cells (2 x 10(6)/mouse) in recipients preconditioned with total-body irradiation (200 R weekly for 3 weeks). Tumors appeared five to ten days postimplant and reached up to 25% of body weight after a mean survival of 8 weeks (range, 30 to 90 days). Tumor histology suggested large cell lymphoma. Cytochemically and immunophenotypically, tumor cells were indistinguishable from their parent cells. Species and lineage derivation of tumor cells was confirmed by antibody probes against the mouse histocompatibility antigen H-2, human T and B lymphocyte antigens, and the HCL-associated common chronic lymphocytic leukemia antigen (cCLLa). In order of decreasing frequency, metastases occurred in the spleen, lungs, pleura, lymph nodes, bone marrow, and kidneys. Up to 12% of circulating lymphoid cells in mice were cCLLa-positive, which suggested hematogenous tumor dissemination. This HCL xenotransplantation model might be useful in preclinical studies for exploring novel experimental therapies for the management of human HCL.