A method for preparing and isolating a transformation vector containing CSF/cDNA is described. The method comprises: preparing RNA from a cell that produces CSF; preparing polyadenylated messenger RNA from the RNA; preparing single stranded cDNA from the messenger RNA; converting the single stranded cDNA to double stranded cDNA; inserting the double stranded cDNA into transformation vectors and transforming bacteria with the vector to form colonies; picking pools of 200 to 500 colonies each and isolating plasmid DNA from each pool; transfecting the plasmid DNA into suitable host cells for expressing CSF protein; culturing the transfected cells and assaying the supernatant for CSF activity; and selecting CSF positive pools and screening the colonies used to make the pool to identify a colony having CSF activity. Also described are a cDNA coding for a protein having CSF activity (i.e. CSF/cDNA), a microorganism or cell line transformed with a recombinant vector containing such CSF/cDNA, and a method for producing CSF protein by expressing said CSF/cDNA by culturing a microorganism or cell line.