After the 1972 mercury poisoning in Iraq, there was widespread concern over the use of mercury fungicides in seed dressing. The ethyl mercury fungicide Ceresan M, claimed to be responsible for the two earlier outbreaks of poisoning in 1956 and 1960 in Iraq, was tested in Drosophila to study its mutagenic potentialities. Of the two concentrations used, namely 30 and 40 mg of the chemical in 100 cc of the food medium, the latter treatment resulted in a significant increase in the frequency of sex-linked recessive lethals.