This is the seventh in a unique series of fasicles comprising an international classification of rodent tumors which provides information and guidelines for international use in practical toxicologic pathology. In a concise, easy-to-use format, essential information on each lesion is presented with typical micorgraphs selected from both spontaneous and induced lesions. The complete range of organ systems in the rat is covered in the series of 10 fasicles. Fasicle 7 covers the central nervous system, heart, eye, and mesothelium. This classification will harmonize and standardize the nomenclature and diagnostic criteria to be used worldwide for regulatory purposes.