This is the second edition of the third volume in the Monographs on Pathology of Laboratory Animals series. Since the first edition, new information has developed at a remarkable pace. Both editions propose standardized nomenclature that is being used internationally, gaining significant acceptance. The result is improved communications of pathologic data to regulatory agencies and in scientific publications worldwide. New information on the nature and variability of preneoplastic lesions in the liver of laboratory rodents is included in this edition. The book expands data on the accompanying changes in enzyme activity in affected liver cells. Spongiosis hepatis in the rat and its relation to spongiotic pericytoma are discussed thoroughly. Information on many other pathologic entities is brought up to date and new ones are added to this second edition, making it an even more useful and expanded reference text.