Abstract: It is described a hybrid molecule of formula GM-CSF-L-EPO or EPO-L-GM-CSF useful for the stimulation of hematopoiesis, comprising GM-CSF and EPO molecules fused together by means of a linker L having a variable length of amino acids, GM-CSF and EPO molecules being either complete molecules or fragments thereof. Such hybrid molecules exhibit a higher specifity of action on erythroid differentiation if compared to that of an equimolar mixture of not-linked GM-CSF and EPO molecules. Further, the present invention describes: DNA sequences encoding such hybrid molecules, which stimolate the hematopoiesis; plasmid vectors containing the genes encoding hybrid molecules and directing their synthesis in host cells; the use of such hybrid molecules for the preparation of a pharmaceutical composition and such pharmaceutical composition useful for stimolation of hematopoiesis.