The invention relates to the process for the isolation of biologically active granulocyte colony stimulating factor (G-CSF), which enables the separation of correctly folded biologically active monomeric molecules of G-CSF from the incorrectly folded, biologically inactive monomeric, oligo- or polymeric and also from aggregated molecules of G-CSF by using immobilised metal affinity chromatography. The process of the invention, if desired the whole process, can be advantageously performed under native conditions. The biologically active G-CSF with a purity of greater than 95% is thus obtained. Only two additional chromatographic steps, cationic exchange chromatography and gel filtration, are then preferably applied to remove the traces of impurities. The entire process results in the production of higher yields of G-CSF with a purity of greater than 99%. The described process is particularly suitable for the industrial production of G-CSF.
