AbstractWe examined the effects of recombinant human tumor necrosis factor (rhTNF) on normal human and murine granulocyte‐macrophage (CFU‐gm) and erythroid (CFU‐e, BFU‐e) progenitor cells. We suppressed in vitro colony formation by human marrow CFU‐gm, CFU‐e and BFU‐e or peripheral blood BFU‐e by adding rhTNF to the culture in a dose‐related manner. A half‐maximal inhibition was observed with 1–10 ng/ml. Leukemic cell line K562 cells were found to be sensitive to rhTNF in the clonogenic colony assay. However, the clonal growth of murine marrow CFU‐e and BFU‐e colonies was less than 50% inhibited and CFU‐gm growth was unaffected even at a concentration of 1,000 ng/ml. We observed slight to moderate inhibition after 24 h pulse exposure of both human and murine‐committed progenitors to rhTNF prior to the culture. Intravenous injection of 1 mg/kg of rhTNF caused a marked decrease in marrow erythroid progenitors and consequently caused anemia in the mice. Our data indicate that rhTNF has a suppressive effect on normal human and murine hemopoietic colony formation in vitro and