The present invention provides a method for stable long-term storage of non-glycosylated recombinant human Granulocyte-Colony Stimulating Factor (“G-CSF”), wherein an aqueous acetate or glutamate buffered G-CSF composition containing the non-glycosylated recombinant human G-CSF and sorbital is cooled to a temperature of −15° C. or below to obtain a frozen G-CSF composition, which frozen composition is then stored in the frozen state and then increased in temperature to a temperature within the range of from 2° C. to 8° C. for a period of time adjusted to allow the composition to thaw and to obtain a liquid composition having a G-CSF content of at least 95% of the G-CSF content of the original composition.
