Six times since 1964, the Public Health Service has issued formal reviews of the scientific evidence which links cigarette smoking to disease and premature death. Each successive review, including this one, has seemed to confirm and strengthen the conclusion of the 1964 Report, that cigarettes are a major cause of death and disease. In the first three chapters of this report, the relationships between cigarette smoking and cancer, cardiovascular disease, and non-neoplastic bronchopulmonary disease are reviewed and evidence is presented which helps develop our understanding of the mechanisms which are involved in these relationships. In the final three chapters, information is presented on public exposure to air pollution from tobacco, on the relationship between tobacco and allergy, and on the harmful consituents which are found in cigarette smoke. The chapter which discusses the harmful constituents of smoke is a useful statement of our current knowledge in this field. (Author)