Sulfadiazine sodium is a sulfonamide?antibiotic with antimalarial activity. Sulfadiazine can be used for toxoplasmosis research[2].In Vivo: In this study, the effectiveness of Sulfadiazine sodium and Pyrimetamine for the treatment of mice during acute infection with different atypical T. gondii strains was evaluated. Swiss mice were infected with seven T. gondii strainsl. The infected mice were treated with 10-640?mg/kg per day of Sulfadiazine sodium, 3-200?mg/kg per day of Pyrimetamine, or a combination of both drugs with a lower dosage. A descriptive analysis was used to assess the association between susceptibility to sodium and/or Pyrimetamine and the genotype. The TgCTBr4 and TgCTBr17 strains (genotype 108) presented lower susceptibility to sodium or Pyrimetamine treatment. The TgCTBr1 and TgCTBr25 strains (genotype 206) presented similar susceptibility to PYR but not sodium treatment. The TgCTBr9 strain (genotype 11) was the only strain with high susceptibility to treatment with both drugs .