The effects of methylprednisolone sodium succinate and cytarabine have been examined in an experimental herpes simplex virus-induced encephalitis in rabbits. In this model herpes simplex virus (HSV) is normally cleared from the brains of untreated animals. Infected animals treated with large doses of methylprednisolone showed a slight delay in the rate of clearance of virus, and a minimal reduction in the inflammatory process, but did not otherwise differ from untreated controls. Animals treated with cytarabine displayed a notable rise in viral titers in brain at a time when virus had been cleared from untreated controls. Cytarabine-treated animals also showed persistence of intranuclear inclusions in the lesions, and moderate diminution in the extent of inflammatory response. Thus, while methylprednisolone appears to have little adverse effect on the encephalitic process, cytarabine, perhaps because of its immunosuppressive properties, results in a failure of normal clearance of virus from nervous system lesions.