Dichlorvos has been in widespread use as an insecticide for over 40 years, during which time its carcinogenicity and genotoxicity have been evaluated extensively. In vitro genotoxicity assays--have shown dichlorvos to be a direct acting genotoxicant at high concentrations, consistent with its known chemical reactivity. This activity is greatly reduced in the presence of S9-mix providing auxiliary metabolic activation, again consistent with its known chemistry and metabolism. Dichlorvos has been examined in a number of in vivo genotoxicity assays using a range of cell types and endpoints, and whilst there are some reports of activity, a critical evaluation has shown that there is no convincing evidence that dichlorvos has significant genotoxic activity in vivo under exposure conditions relevant to potential human exposures. In combination with the extensive carcinogenicity database for dichlorvos, the weight of evidence indicates that dichlorvos is not genotoxic under exposure conditions relevant to those that might occur in humans.