<正> Monoclonal antibodies against gastric cancer（MG）were purified by ion-exchangechromatography on DEAE-cellulose（DE-52）column and coupled with CNBr-activated Sepharose4B.The Sepharose 4B linked with MG monoclonal antibodies was then incubated with serum andascitic fluid of patients with gastric cancer and benign diseases for 2h.After being blocked by nor-mal mouse serum

the MG-Sepharose was mack to react with the MG-labeled with fluoresceinisothiocyanate for 30min.According to immunoaffinity chromatography principle

the MG-labeledwith fluorescein isothiocyanate was separated from the MG-Sepharose with 0.01 mol/L of PBS-3mol/L of KCNS solution and then detected with a fluorospectrometer.The amount of fluorescencein the solution of separation represented the amount of the antigens defined by MG monoclonalantibodies.The mean value plus 2 standard deviations of the benign disease group was arbitrarilyset as their positive threshold.The positivity rates were 61.1%（22/36）in serum and 75%（18/24）inascitic fluid of patients with gastric cancer.It suggests that the determination of MG-Ags in the se-rum and ascitic fluid of patients may be helpful for the diagnosis of gastric cancer.