cDNAs encoding human interleukin 3, colony stimulating factor 2 (granulocyte-macrophage) and kit ligand were independently ligated into expression cassettes in which the cDNA resides downstream of the cytomegalovirus (CMV) promoter/enhancer sequence and is followed by human growth factor intronic and polyadenylation sequences. A transgenic mouse that was shown by ELISA to have serum levels of all three growth factors at ng/ml levels was used to establish a line with the same phenotype.