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 gave positive results for gene reversion and conversion in yeast that 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 alkylate DNA of mice exposed through inhalation and may have caused unscheduled DNA synthesis in kidneys of similarly exposed mice. The studies on the mutagenicity of vinylidene chloride are evaluated in this review.