Antisera prepared against Ca, CC, ECH44, FH5, G278, L279, LAZ238, P, PM120, and T strains of Trypanosoma cruzi by immunization of rabbits with culture forms can be classified into three groups (A, B, C) on the basis of their reactivity in double diffusion agar gel and immunoelectrophoresis plates after absorption with strain-type antigens. Reactions before absorption were too complex to permit classification of the strains. The strains were all pathogenic originally, regardless of their group classification. © 1969.