The Thermal Insulation Manufacturers Association (TIMA), a trade association whose membership includes companies producing fibrous glass products, wishes to advise the Environmental Protection Agency with respect to an interim study report most recently obtained in an ongoing study sponsored by the Association and its membership. In the fall of 1977, TIMA agreed to sponsor with the Lost Alamos National Laboratory a study concerned with animal exposures to assess the potential health effects of various man-made vitreous fibers. As part of this study, a group of 24 female Osborne-Mendel rats were injected intraperitioneally with very fine diameter fibrous glass. Eight of these 24 animals developed mesotheliomas. These findings are useful, but were not unexpected. Similar findings have been reported by numerous investigators both in this country and abroad.