Ethylene glycol monomethyl ether (EGME) or 2-methoxyethanol (2-ME) is a toxic compound that has teratogenic effects in developing organisms similar to its oxidation product methoxyacetic acid (MAA). Alcohol dehydrogenase (ADH) is supposed to be involved with the oxidation of EGME into MAA. It has been shown here that Drosophila ADH dehydrogenates EGME in an in vitro test system. Three strains of Drosophila melanogaster, genetically different from each other with regard to ADH activities (qualitatively and quantitatively), were used to test the in vivo involvement of ADH with the oxidation of EGME into MAA. The toxicity of EGME in egg-to-adult and third instar larval-to-adult development is concentration and strain dependent. Higher detoxification occurs in the strain with increased ADH activity. EGME is much more toxic than its oxidation product MAA at the level of adult eclosion. Teratogenic effects were observed in the ADH-negative strain in spite of lacking ADH activity. EGME is apparently a teratogenic compound by itself.