The Thermal Insulation Manufacturers Association (TIMA) is a trade association that includes manufacturers and users of manmade refractory fibers. The Carborundum Company, as a member of TIMA and a manufacturer of refractory (ceramic) fibers, contributed to the conduct of a chronic inhalation study of refractory (ceramic) fibers in Syrian Hamsters and Osborne-Mendel Rats. The contractor has orally reported to us the occurrence of a single malignant mesothelioma in a hamster which died in the ninth month of the two-year study. The study is being conducted with 80 hamsters and 64 rats. Since the tumor could have occurred spontaneously or from other causes, its significance cannot be determined prior to completion of the study. The inhalation study is being conducted at the Los Alamos Scientific Laboratories under the direction of Dr. David Smith. It was Dr. Smith's opinion that no biological conclusion could be reached at this time and that the single occurrence was not statistically meaningful. This opinion has been supported by the Health and Safety Group (TIMA), Medical and Scientific Committee (TIMA) and various medical and toxicology experts within The Standard Oil Company (Ohio)-Carborundum's parent company. Thus, it is our view that this information does not represent a reportable substantial risk under Section 8(e) of the Toxic Substances Control Act.