A cell line, designated HAL-01, was established from the blood cells of a patient with acute lymphoblastic leukemia (ALL) with a myeloid-associated marker. Both the cell line and the patient's fresh leukemia cells had the chromosomal translocation t(17;19)(q21;p13). Morphologically and cytochemically, the cells were lymphoid in appearance. Immunophenotyping of the donor's leukemia cells revealed that they express B lineage antigens (CD10+, CD19+, CD20+, CD22+); the myeloid-associated antigen (CD13) detected in the donor's leukemia cells was not expressed by the established cell line. The HAL-01 cells have a rearrangement of the immunoglobulin heavy chain gene, while the T-cell receptor beta-chain genes remain in the germline configuration. The gene encoding the binding proteins for the kappa-light chain enhancer (kappa E2), which is involved in pre-B-ALL cells with the t(1;19) (q23;p13) translocation, is not rearranged in the cell line. The HAL-01 cells were transplantable into the peritoneum of untreated nude mice where they grew as an ascites tumor. The growing tumor cells also infiltrated lymph nodes, liver, spleen, kidney, and bone marrow without exhibiting a particular change in the morphology of the neoplastic cells. Clonogenic assay in methylcellulose culture demonstrated that the proliferation of the HAL-01 cells was suppressed by interleukin-3 (IL-3) in a dose-dependent fashion, with maximum inhibition occurring at concentrations greater than 100 U/ml. Treatment with IL-3 reduced the number of viable cells as well as induced morphological changes without concomitant changes in cytochemical reactions or immunophenotypic expression. Reduction of 3H-thymidine incorporation by exposure of IL-3 was blocked by the pretreatment of neutralizing anti-IL-3 antibody, but not by neutralizing anti-TGF-beta antibody. Thus, HAL-01 is a unique ALL cell line exhibiting proliferative suppression by IL-3 that may prove useful in studying the interactions of cytokines in ALL.