Strains of D. melanogaster derived from a vineyard population were more resistant to alcohol in the environment than strains from a population derived from an area removed from the vineyard. Within the vineyard population those strains most closely associated with alcohol in the environment in the cellar were more resistant than those collected outside the cellar. There was evidence of gene flow between the inside and outside cellar components of this population, but microdifferentiation had occurred within the cellar in spite of this. The adaptation appears to be independent of the ADH system and involves both additive and dominance genetic effects. D. simulans, a species not found in the cellar and susceptible to the presence of alcohol, showed no differentiation between vineyard and removed populations.