A biometric study of ien strains of T. cruzi isolated from human cases of Chagas' disease showed a great deal of strain variation. Thus the values of the mean total lenght of different strains varied from 16,3μ, to 21,8μ. while the values of the mean nuclear index varied from 0,93 to 1,52. These results, specially those on the mean nuclear index, indicate that the limits of strain variations in T. cruzi are wider than those previously observed.