Symbiotic relationships between microbes and animals are ubiquitous in nature. The animal microbiota is a vast and diverse population of bacteria and other microbes living symbiotically with their hosts that has a profound influence on many aspects of host physiology, including metabolism, immunity, development, and behavior. However, little is known about the molecular crosstalk between microbes and host that mediate these effects, particularly in the area of brain function and behavior. To address this problem, we employed a proteomic technique call Two-dimensional Difference Gel Electrophoresis (2D-DIGE) to examine the protein differences in heads between conventionally-reared (CV) flies and “germ free” (GF) flies, those raised in a sterile environment. We found that the level of Alcohol Dehydrogenase (ADH), a key enzyme in alcohol metabolism, is elevated in the heads of GF males and females, suggesting that GF flies would be less sensitive to the effects of ethanol (EtOH) exposure. Indeed, we found that GF males are significantly less sensitive (T50=16.4 mins) to the immobilizing effects of EtOH vapor than their CV counterparts (T50= 11.8 mins). This increased EtOH sensitivity is partially reverted when restoring the normal Drosophila microbiota to GF flies 0-24 hours after eclosion. This suggests that the microbiota plays an important role in the response of Drosophila to EtOH vapor. We are currently testing whether the microbiota also affects EtOH recovery, tolerance, and preference in Drosophila. These data provide a new insight on the effect of the microbiota on alcohol metabolism that may lead to a deeper understanding of the microbiota’s role in alcoholism. .