The alcohol dehydrogenase (ADH) activity and ADH cross reacting material (ADH CRM) were measured and Northern blot analysis was carried to define the function and the regulation mechanism of the Adh gene. This study examined how dietary threonine affects the expression of the Adh gene during development of Drosophila melanogaster. Two wild type strains, one homozygous for Adh(F) and one for Adh(S) from Chunan, Korea were used. The ADH activity and CRMs of the Adh(F) strain were 2.1 times higher than those of Adhs strain, and ADH activity was higher with isopropanol (secondary alcohol) than with ethanol (primary alcohol) as a substrate in both Adh(F) and Adh(S) strains. When the larvae, pupae, newly emerged adults (0-1 day), and adults (5-7 days) of Drosophila melanogaster Adh(F) and Adh(S) strains were fed on a defined low yeast and threonine medium, ADH activity and ADH CRM levels were increased. Northern blot analyses indicated that the production of mRNA of the larvae, young adults (0-1 day), and adults (5-7 days) was increased by dietary threonine. ADH activity and ADH CRM increases in Drosophila melanogaster fed on threonine were as a result of threonine-stimulated alteration in the amount of ADH mRNA. The elevated level of the ADH mRNA transcribed from the proximal and distal promoters of threonine-fed larvae and adults showed that there was an induction.