Abstract: Diphtheria toxoid is denatured in 0.1M NE₄Cl-NH₃·H₂O basal solution with pH9.4, yielding a cathodic and an anodic polarographic peaks at-1.50 and-1.46 V(vs.SCE) respectively.The cathodic and anodic peak heights vary linearly with diphtheria toxoid concentration over the range of 2.5 to 180 μg/ml by single sweep polarography; and even as low as 0.3μg/ml, diphtheria toxoid could be detected by differential pulse polarography. The decreased peak current value of diphtheria toxoid is proportional to diphtheria antitoxin present due to immuno-chemical binding reaction in the range of 2.5×10^-6to 5×10^-5IU/ml,which determines diphtheria antitoxin level homogencausly. The assays are sensitive specific, resproducible in operation The anodic peak has been applied to the determination of diphtheria toxoid in the triple vaccine.