Several compounds are associated with experimentally induced neoplasms in the urinary systems, and especially the kidneys, of laboratory animals. Many of these neoplasms are succintly described and illustrated in detail in this volume, and some are compared with spontaneously occurring lesions. Pragmatic aspects of disease which are of particular interest to pathologists are emphasized, such as classification and differential diagnosis of neoplasms that occur in the urinary system; comparison and significance of toxic effects of substances in animals and humans; and similarities and differences in disease manifestations between animals and humans.