A large number of studies indicate that vinylidene chloride is mutagenic to bacteria and that this activity is largely dependent on microsomal activation. Vinylidene chloride was reported to produce positive results for gene reversion and conversion in yeast, which was also dependent on metabolic activation, and was positive in tradescantia. In mammalian systems vinylidene chloride failed to induce gene mutations in V79 cells at two separate loci, failed to induce chromosomal aberrations in mouse bone marrow in vivo, and failed to induce dominant lethals in either mice or rats. Vinylidene chloride was found to bind to DNA of mice exposed through inhalation and may have caused unscheduled DNA synthesis in the kidneys of similarly exposed mice. Analysis of the data relating to the potential of vinylidene chloride to behave as a human germ-cell mutagen indicates that, based on the criteria established in EPA's Proposed Guidelines for Mutagenicity Risk Assessment, the evidence at the present time is classified as limited.