This thesis describes my study of inhibition of brain regeneration in planaria. The flatworm (Dugesia tigrina) possesses a remarkable ability to regenerate lost parts, including the head. The primary objective of my study was to determine the extent to which an inhibiting substance, located in the head, would prevent regeneration of the brain. A secondary objective was to study whether DMSO (Dimethyl Sulfoxide) would facilitate the action of the inhibitor.