We studied the interaction of interleukin (IL)‐4 and other burst‐promoting activity (BPA) factors, such as IL‐3, granulocyte/macrophage colony‐stimulating factor (GM‐CSF), IL‐9 and stem cell factor (SCF), on erythroid burst‐forming unit (BFU‐E) and erythrocyte‐containing mixed (CFU‐Mix) colony formation in serum‐free culture. IL‐4 alone did not support mixed colony formation in the presence of erythropoietin (Epo). However, IL‐4 showed weak but significant BPA when peripheral blood (PB)‐derived CD34+c‐kitlow cells were used as the target population. The BPA of IL‐4 was much weaker than that of IL‐3, which exerted the most potent activity, as previously reported. When CD34+c‐kithigh cells were used as the target, four factors known to have BPA, IL‐3, GM‐CSF, IL‐9 and SCF, could express BPA. In contrast, IL‐4 alone failed to support erythroid burst formation. Interestingly, IL‐4 showed a remarkable enhancing effect with SCF in promoting the development of erythroid burst and erythrocyte‐containing mixed colonies from CD34+c‐kitlow and CD34+c‐kithigh cells. Delayed addition of SCF + Epo or IL‐4+Epo to the cultures initiated with either IL‐4 or SCF alone clearly demonstrated that SCF was a survival factor for both BFU‐E and CFU‐Mix progenitors. In contrast, the survival effect of IL‐4 was much weaker than that of SCF, and appeared to be more important for progenitors derived from CD34+c‐kitlow cells than for those derived from CD34+c‐kithigh cells. It was recently reported that CD34+c‐kitlow cells represent a more primitive population than CD34+c‐kithigh cells. Taken together, these results suggest that IL‐4 helps to recruit primitive progenitor cells in the presence of SCF.