The open treatment groups are: Atovaquone plus pyrimethamine for patients with acute toxoplasmic encephalitis who have no treatment limiting toxicity to pyrimethamine, and Atovaquone plus clarithromycin for patients with acute toxoplasmic encephalitis who have treatment limiting toxicity to both pyrimethamine and sulfadiazine. The following arms closed on 12/22/95: Randomization to the atovaquone plus sulfadiazine arm for patients with acute toxoplasmic encephalitis who had no treatment limiting toxicity to pyrimethamine or sulfonamides, and Atovaquone plus sulfadiazine for patients with acute toxoplasmic encephalitis who had treatment limiting toxicity to pyrimethamine. The following arm closed on 9/26/95: Atovaquone plus pyrimethamine for patients with acute toxoplasmic encephalitis who had treatment limiting toxicity to sulfonamides. NOTE: Any patients enrolled in previous versions will continue to be treated with that same drug treatment and followed under their previous version guidelines.