Critical issues in the design, evaluation and interpretation of long-term animal carcinogenicity studies are addressed in this volume. The presentations are by top pathologists, toxicologists and statisticians in the USA, Canada and Europe, representing industry, academia and regulatory agencies. The discussions involve controversial as well as conventional issues and are presented from statistical and biological or toxicological perspectives. Although more work has been done and published on long-term animal carcinogenicity studies than in any other phase of chemical or drug safety assessment, many issues still remain unresolved. Some solutions have been proposed, but in many instances they have not proven to be completely remedial. This volume continues important discussion of these issues and proposed solutions, and should be of interest to scientists engaged in long-term animal carcinogenicity testing.