Toxoplasmosis encephalitis developed in three male homosexuals with AIDS. Clinical symptoms of encephalitis began with a nonspecific organic mental syndrome. In two cases there developed late focal symptoms. There were light to moderately severe generalized EEG changes with additional focal signs. CSF findings and toxoplasmosis titres were not diagnostically altered. Computed tomography demonstrated multiple areas of decreased density in cortex and cerebellum. Administration of pyrimethamine and sulfamethoxydiazine to the three patients brought about clinical improvement within a few days and regression of abnormal CT changes within a few weeks of onset of treatment. One patient died after an encephalitis recurrence: autopsy demonstrated toxoplasma pseudocysts in immediate proximity to small necrotic foci in the brain. The possibility of toxoplasma encephalitis should be considered in AIDS patients who develop an organic mental syndrome. Often the diagnosis can only be made after response to a trial of toxoplasmosis treatment.