A summary of preliminary results from a lifetime skin painting carcinogenicity assay on mice treated with XB-2793, a mixture containingabout 70% 2,4-imidazolinedione,5,5- dimethyl-1,3-bis (oxiranylmethyl)-C11H16O4 and 30% 2,4-imidazolidiendione, 5,5-dimethyl-, polymer with chloromethoxirane andmethyloxirane. At 24 treatment months, gross observations revealed skin tumors at the application site. In vitro mutagenicity screening assays of this product with Salmonella typhimurium showed evidence of mutagenicactivity in 3 of 4 test batches, both with and without metabolic activation, and no evidence of mutagenicity for the other batch. Furthertests with this latter batch gave positive results in the L5178Y mouse lymphoma assay and negative results with Saccharomyces cerevisiae, both with and without activation. S. typhimurium plate assays of a second product, XB-2826, a mixture containing predominantly XB2793, with some 4,4'-(1-methylethy lidene)bisphenol, showed evidence of mutagenesis both with and without metabolic activation, and assays with C. cerevisiae were negative for mutagenic activity. Further experimental details were not provided.