In previous studies, we have demonstrated that progenitor cell-enriched marrow cell populations from patients with myeloid leukemia - including both acute (AML) and chronic (CML) - show severe functional alterations when cultured in stroma-free liquid cultures supplemented with stimulatory cytokines. In trying to expand our characterization of the biology of leukemic cells, in the present study we have used a similar approach and analyzed the in vitro growth of equivalent cell populations from patients with acute lymphoblastic leukemia (ALL). ALL marrow cell populations -enriched for hematopoietic progenitors by means of a negative selection procedure- were assessed for their proliferation and expansion potentials, in liquid cultures supplemented with a mixture of early- and late-acting recombinant stimulatory cytokines, throughout a 25-day culture period. ALL cells, although capable of responding to the stimulatory signals provided by hematopoietic stimulators, showed deficient proliferation potentials (reduced capacity to generate more nucleated cells), as compared with their normal counterparts. The capacity to generate myeloid and erythroid progenitors was also significantly reduced in ALL cultures. Interestingly, the functional alterations observed in ALL cultures (i.e., deficient proliferation and expansion potentials) were more pronounced in those from Ph+ patients than in those from Ph- patients. This study indicates that bone marrow cell populations - enriched for hematopoietic progenitor cells - from ALL patients possess deficient proliferation and expansion potentials in vitro, and that such functional alterations are more severe when cells are derived from Ph+ patients, as compared to their Ph- counterparts.