The establishment of the National Center for Toxicological Research (NCTR), Jefferson, Arkansas [USA], to study long term effects of low doses of potentially toxic substances, including carcinogens, resulted in the initiation of chronic experiments requiring histopathologic studies of large numbers of animals. Processing the tissues and recording and analyzing the massive amount of pathologic data from these studies required innovative automated techniques. The result was a unique computerized pathology data system at NCTR. The system encompasses the development of training programs for necropsy technicians, histology technicians and pathology tissue screeners; the use of automated equipment for processing, embedding, sectioning and staining tissue; the use of prelabeled cassettes, slides and pathology forms; the use of mark-sensitive forms for the collection of gross and microscopic findings; the use of data collection terminals for animal identification, animal weights and organ weights; the collection of gross and microscopic data on a Mod Camp III minicomputer; and the storage, analysis and generation of pathology reports and tables over a data link from an IBM 370-158 computer. Some of the features of this system may be applicable in other toxicology laboratories and medical pathology departments.