AbstractThe effects of recombinant interleukin‐6 (rIL‐6) and rIL‐3 on the radiation responses of myeloid [colony forming unit‐granulocyte‐macrophage (CFU‐GM)] and erythroid [burst forming unit‐erythroid (BFU‐E)]human pediatric bone marrow progenitor cells were analyzed. Cytokine exposure times of 30 min, 1 hr, 2 hr, 4 hr, 16 hr, and 24 hr were used prior to irradiation. The most notable observations were based on short exposure data, which provided unprecedented evidence that rIL‐6 increases the radiation damage repair capacity of both CFU‐GM and BFU‐E without affecting their radiation sensitivity, whereas rIL‐3 modulated the radiation responses of CFU‐GM only. The cytokine‐induced increase in radiation survival of CFU‐GM or BFU‐E at doses ≤200 cGy appeared to be primarily due to an increase in the ability of these hematopoietic progenitor cell populations to