Antigenic potential of genetically engineered human granulocyte colony-stimulating factor (CJ-50001) was assessed in guinea pigs and mice. In active systemic anaphylaxis (ASA) test, although CJ-50001 at 50 $mu extrm{g}$ /head induced anaphylactic responses, CJ-50001 5 $mu extrm{g}$ /head alone or 50 $mu extrm{g}$ / head with adjuvant did not induce anaphylactic responses. In passive systemic anaphylaxis test (PCA) or passive hemagglutination test (PHA), CJ-50001 did not induce positive responses. It is concluded that, in light of the fact that CJ-50001 was antigenic only in ASA but not in PCA or PHA and also that CJ-50001 is a foreign human recombinant protein to guinea pigs, CJ-50001 may not induce systemic allergic react-ion in its clinical use in human.