Mobil Chemical Company compound MCTR-4-79 (MRI no. 221) was received on February 26, 1979, for testing in the Salmonella/mammalian-microsome mutagenicity assay using five tester strains, TA98, TAl00, TAl535, TAl537 and TAl538, both with and without metabolic activation by rat liver microsomes. The experimental protocol is a modification of that described by Ames, B. N., et al. Methods for detecting carcinogens and mutagens with the Salmonella/ mammalian-microsome mutagenicity test are used. In terms of reportable substances our submission is organized and may be summarized as follows: Chlorinated Paraffin, Toluene, Epoxides, Phthalate ester, Xylene, Methyl Ethyl Ketone, Methyl Isobutyl Ketone, Propylene Oxide, Trieresyl Phosphate, and Trixylenyl Phosphate.