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