Abstract: It is well known that penicillins are necessary for prevention of contamination during cell culture or fermentation in the production of gene engineering drugs. As penicillins are easily combined with proteins forming allergic impurities, the benzyl penicilloyl proteins in aqueous solution, an evaluation system should be established for control of the gene engineering drugs. An enzyme linked immunosorbent assay (ELISA) with high specificity and high sensitivity in vitro, by which the conjugated penicillins of 0.3 ppm in a sample could be detected and a passive cutaneous anaphylaxis (PCA) test, a classical method for evaluation of allergic reaction in vivo are integral parts of this system.Some domestic gene engineering drugs such as erythropoietin (EPO), G-CSF, GM-CSF and ¹²⁵SerIL-2 are evaluated with this system. No matter whether the expression products was produced in secretion manner or in inclusion body, it was possible that some residues of allergic impurities may remain in the finished products if an unsuitable process of isolation and purification was used. The maximum absolute content of the conjugated penicillins in a sample was up to about one per thousand.