The aim of this study was to test whether colony stimulating factors (CSF) and other cytokines facilitate the recovery of a variety of immunohematopoietic functions in lethally irradiated mice undergoing bone marrow transplantation (BMT). Two experimental systems were employed: (a) lethally irradiated mice transplanted with syngeneic or T cell-depleted semi-allogeneic bone marrow (BM) cells (0.1-10 x 10(6)), subsequently treated by multiple doses of cytokines; and (b) lethally irradiated mice transplanted with BM cells that had previously been cultivated with cytokines. The cytokines used were: pure natural mouse interleukin-3 (IL-3); recombinant mouse granulocyte-macrophage CSF (rGM-CSF); recombinant human interleukin-2 (rIL-2); and crude cytokine preparations obtained from the culture supernatants of murine leukemia WEHI-3b cells (containing mainly IL-3), and of phorbol myristate acetate (PMA)-stimulated EL4 leukemia cells and concanavalin A-stimulated rat splenocytes (each containing a multitude of cytokines). For BM cultures (1-9 days), the cytokines were used at a dosage of 1-100 U/ml; for in vivo treatment, 2 x 10(2)-5 x 10(4) units were administered intraperitoneally and subcutaneously at different schedules for varying periods (1-3 weeks). The following parameters were tested 1-10 weeks post-BMT: white blood cell count, colony formation in agar and in the spleen of lethally irradiated mice, proliferative responses to mitogens and alloantigens, allocytotoxicity and antibody production (serum agglutinins and plaque-forming cells) against sheep red blood cells. Under appropriate conditions, cytokine treatment either in vitro or in vivo significantly enhanced (2- to 50-fold compared with controls) most functions tested at 2-8 weeks post-BMT, and shortened the time interval required for full immunohematopoietic recovery by 2-5 weeks. In recipients of semi-allogeneic, T lymphocyte-depleted BM no evidence of graft-versus-host disease was found. It is suggested that judicious application in vitro and/or in vivo of certain pure cytokines (e.g. GM-CSF, IL-3) or cytokine 'cocktails' might be beneficial in enhancing hematopoiesis and in the treatment of immunodeficiency associated with BMT.