SummaryExperimental infection by toxoplasma in the mouse has been treated by trimetoprim-sulfamethoxazol association. All animals are survived ; besides that, they have acquired an immunity against a reinfection by the same parasite. The in vitro experiments have demonstrated that this acquired immunity depends on humoral and cellular factors.The clinical experience, even limited, confirms the results of the laboratory. The association trimetoprim-sulfamethoxazol can be proposed as a new therapeutic of the toxoplasmosis.