In order to evaluate the mutagenic potential of CJ-50001 (recombinant human granulocytecolony stimulating factor), 3 sets of mutagenicity tests were performed. In the reverse mutation test using Salmonella typhimurium TA1535, TA1537, TA98 and TA100, CJ-50001 did not increase the number of revertant at any of the concentration tested in this study (500, 250, 125, 62.5 and 31.3 $mu extrm{g}$ plate). CJ-50001, at the doses of 200, 100 and 50 $mu extrm{g}$ /ml, did not increase the number of cells having structural or numerical chromosome aberration in cytogenetic test using Chinese Hamster Lung cells. In mouse micronucleus test, no significant increase in the occurrence of micronucleated polychromatic erythrocytes was observed in ICR male mice intraperitoneally administered with CJ-50001 at the doses of 5, 2.5 and 1.25 mg/kg. These results indicate that CJ-50001 has no mutagenic potential in these in vitro and in vivo systems.