A comparative analysis was made of the histological changes caused by Corynebacterium Parvum (C. parvum) infected into the brain and dermis of normal and C. parvum presensitized rats. Control rats were injected with saline. It was shown that for approximately 3 days after the intracerebral injection the brain reacted with a polymorphonuclear cell infiltration. This reaction was replaced in order by lymphocytes, macrophages, and finally by epithelioid cells progressing to granuloma. The histological changes were similar but more intense in the dermis than in the brain. Lymphocytes reached a peak by day 7, macrophages by day 3, and epithelioid cells by day 18. In comparison to the dermis, the cellular infiltration in the brain is more delayed, less intense and of longer duration. Intracerebral saline induced a moderate lymphocytic infiltrate, and in C. parvum presensitized rats a more intense macrophagic response. It is concluded that the brain of the rat, especially in presensitized animal, mounts an inflammatory response to C. parvum which is morphologically similar to that seen in the skin.