The effectiveness of five treatment regimens was compared to mice during acute and late infection with Toxoplasma gondii. Parasitic cure rates, as judged by failure of brain tissue from surviving mice to produce infection when inoculated into clean mice, were as follows: pyrimethamine + sulfamethoxypyridazine, 92%; clindamycin + sulfamethoxypyridazine, 75%; spiramycin + sulfamethoxypyridazine, 16.7%; trimethoprim + sulfamethoxypryridazine alone, 0%. Pyrimethamine + sulfamethoxypyridazine was the most effective combination against acute toxoplasmosis in mice.