The aqueous extract of Trypanosoma cruzi, previously treated by benzene, was filtered throught a column of Sephadex g-200. The eluted fractions were tested by complement-fixation with the chagasic reference serum. It was found that the CF antigens were aluted in the first fractions and the contaminants in the last ones. The aqueous antigen, when dried and extracted with metanol, showed a very high titer in the complement-fixation quantitative test. this antigen is free of contaminants and can be recommended for use in the serological test for the diagnosis of Chagas' disease.