We have developed a new murine model of toxoplasmic encephalitis based on the intracerebral inoculation of tachyzoites of the highly virulent RH strain of Toxoplasma gondii. Intracerebral infection resulted in a mortality of 100% on day five. Large inflammatory abscessed infiltrates developed by the second day after inoculation and expanded throughout the remaining period of observation. Numerous tachyzoites were detectable in brain parenchyma by the second day of infection. The marked and precocious histopathological brain lesions produced by the RH strain are useful to detect therapeutic rather than prophylactic effects of drugs against toxoplasmic encephalitis. In this model pyrimethamine, sulphadiazine and its combination were useful in terms of mortality, histopathology and spread of infection whereas clindamycin showed no activity. This murine model of toxoplasmic encephalitis is useful to evaluate antitoxoplasma agents with high therapeutic activity.