The attached report contains the results of a two year carcinogenesis bioassay of maleic anhydride which was funded by the Chemical Industry Institute of Toxicology and conducted at IIT Research Institute. Several unusual problems occurred during this study. There was a very high incidence of uterine adenocarcinomas in both control and test female rats and there was a 100% incidence of cataracts in both test and control males and females. Although the report speculates that these results may be secondary to continuous lighting for an unknown period prior to the eighteenth month of the study, the potential effects of these problems on the outcome of the bioassay is unknown. In addition, the diets were not analyzed for maleic anhydride until 2-4 years after the study ended. Frozen samples from the high dose group ranged from 44-92% of the expected dose. Maleic anhydride mixed in feed in our facility yielded 95-106% of expected when fresh, and 63-79% after 2.25 years of frozen storage. Maleic anhydride may have converted to maleic acid when mixed in the feed and the animals may not have been exposed to the anhydride. Regardless of these deficiencies this report is being released in accordance with our policy to release all testing program results when a final report is available. It is also our policy to contract for an independent third-party audit of the testing program studies. The audit of this study will be released when completed.