Temperature and ethanol concentration have major effects upon the longevity of adults exposed to ethanol vapour, but do not much influence ADH activity. In contrast, Adh locus genotypes differ in ADH activity quite substantially, while the above two environmental variables have minimal effects. This laboratory result is consistent with certain field results, and emphasizes the need to select phenotypes of direct physiological and ecological importance as primary study materials of natural populations, in addition to conveniently assayable electrophoretic variants.