Different combination of human growth factors were checked for their ability to stimulate human granulocyte-monocytopoiesis in vitro. The optimal combination was found to be: Interleukin -3 (IL-3) + Granulocyte--Monocyte Colony Stimulating Factor (GM-CSF) + kit ligand (KL). In protocols concerning treatment of leukopenias with hemopoietic growth factors is should be concerned the use of combination of above listed growth factors. These growth factors could be added separately or in form of fusion proteins. In the future the efficiency of sequential addition of hemopoietic growth factors should be also evaluated.