Infections caused by Corynebacterium diphtheriae frequently induce situations in 
which very small doses of antigens injected intradermally can cause strong 
inflammatory reactions. This bacterium secretes the diphtheria toxin (DT), a 
virulence factor that can be lethal to the human organism at doses below 0.1 
μg/kg of body weight. The present work proposes alternative methods of DT 
purification using affinity chromatography and of DT detoxification through 
conjugating with the polymer methoxypolyethylene glycol activated (mPEG). Tests 
were performed to evaluate: the formation of edemas and the presence of 
dermonecrotic activity, in vitro cytotoxicity to Vero cells, the neutralizing 
activity of serum from guinea pigs immunized with the diphtheria toxoid 
inactivated with mPEG, and the immunogenic activity of the purified and modified 
toxin. The results indicated that purification with Blue Sepharose was an 
efficient method, yielding antigen purity equivalent to 2600 Lf/mg of protein 
nitrogen. The modification of the Purified Toxin with mPEG did not result in the 
formation of edema or necrosis although it was immunogenic and stimulated the 
formation of antibodies that could neutralize the Purified Toxin. The toxoid 
obtained from the purified toxin maintained its immunogenic characteristics, 
inducing antibodies with neutralizing activity; edema and necrosis were still 
observed, however.