THERE have been several conflicting reports on the genetic effects of Dichlorvos (2,2-dichlorovinyl dimethyl phosphate), which is the active ingredient of Shell's pesticide, ‘Vapona’. Dichlorvos is present in ‘Herkol’, ‘Dedevap’, ‘Oko’, and ‘Mafu’ which are listed as synonyms by Epstein and Legator1. Sax and Sax2 reported chromosome aberrations in onion root tips. Lofroth3 working with pure Dichlorvos demonstrated, in vitro, the alkylation of calf thymus DNA in which N-7-methylguanine was the major product with a yield of 1% after 60 h treatment. According to Epstein and Legator1 who cite the work of Michalek and Brockman4 Dichlorvos is mutagenic in Neurospora. However, this is a mistake, as Michalek and Brockman using the Adenine 3 region of Neurospora crassa were unable to demonstrate any mutagenic effect of Dichlorvos.