AIDS patients with toxoplasmic encephalitis who receive the standard therapy combination of sulfadiazine and pyrimethamine experience a high frequency of severe toxicity. Atovaquone, an antibiotic that has demonstrated efficacy against toxoplasmosis in animal models and in preclinical testing has been well tolerated, is now available as a suspension, which is more readily absorbed than the tablet form of the drug. The efficacy and safety of atovaquone in combination with sulfadiazine or pyrimethamine will be studied.