These are the proceedings of the international symposium on "Experi- mental Respiratory Carcinogenesis and Bioassays", held from 23 to 26 June 1974 at the Battelle Seattle Research Center, Seattle, Wash., USA. Human lung cancer is already very common in industrialized countries, and its incidence is increasing. This increase involves mainly epi- dermoid and small-cell carcinoma. Evidence is accumulating that these tumors are associated with such exogenic factors as automobile exhaust, asbestos, chemicals, cigarette smoke, and radionuclides. These pro- ceedings are concerned with finding the most suitable experimental designs for investigating the genesis of these particular types of tumor, and with the development of specific bioassays to test sus- pected carcinogens. Spontaneous epidermoid and small-cell carcinomas are extremely rare in the respiratory organs of animals, and it has proved rather diffi- cult until recently to produce them experimentally. Epidermoid carci- nomas are now readily obtained by using methods of intratracheal in- stillation of carcinogens with particulate materials such as that described by SAFFIOTTI and co-workers, which is the technique most frequently mentioned in these proceedings. While the experimental production of small-cell carcinomas has remained difficult, it is described by two authors in this volume.