We investigated effects on oral cancer (OC) risk of an interaction between a single nucleotide polymorphism (SNP) in the alcohol dehydrogenase 3 (ADH 3 ) gene and alcohol consumption levels using a hospital-based study of 93 cases and 99 controls conducted in Athens, Greece. This SNP affects ethanol metabolism in vitro and appeared to interact with alcohol consumption in a previous OC study. We also evaluated a SNP in CYP2E1, another gene involved in ethanol metabolism, reported to be associated with OC risk in a European population. Data on genotypes and risk factors obtained from interviews were analyzed using multivariate logistic regression, accounting for potential confounders. No overall (marginal) association was found between OC risk and ADH 3 genotypes. An interaction between ADH 3 genotypes and alcohol consumption levels, however, was suggested. In non-drinkers, the ADH 3 1-1 genotype has higher risk than ADH 3 1-2 or ADH 3 2-2 genotypes, but for subjects consuming alcohol, lower risk was observed for ADH 3 Many epidemiological studies conducted around the world have documented the strong association between increased risk of oral cancer (OC) and heavy alcohol consumption. [1][2][3][4][5] The mechanism by which alcohol causes OC, however, remains unclear. Questions exist about the importance of consumption patterns, alcohol concentration and other components of different beverages and possible carcinogenic metabolites vs. tissue permeability effects in the mode of action. 6,7 Recent reports strongly implicate the metabolite of ethanol, acetaldehyde, as the main carcinogen in OC. Acetaldehyde has been found to cause mutations, form DNA adducts and inhibit DNA repair. 8 -11 Acetaldehyde levels are regulated primarily by 2 enzymatic systems: alcohol dehydrogenase (ADH) that oxidizes ethanol to acetaldehyde and acetaldehyde dehydrogenase that converts acetaldehyde to acetate. Oxidation of ethanol occurs primarily in the liver, but also in the gastrointestinal tract and oral cavity. [12][13][14][15][16] Seven human genes coding for ADH have been identified to date and 3 of these (ADH1, ADH2 and ADH3) are located in a cluster on chromosome 4. 17,18 Single nucleotide polymorphisms (SNPs) that exhibit different enzymatic properties have been reported for some of these ADH genes. 17,19 -22 For example, it has been shown that cells with the ADH 3 1-1 genotype exhibit a V max for ethanol oxidation that is 2.5-fold higher than that that of the ADH 3 2-2 genotype. 19 Ethanol is also metabolized, to a lesser extent, by CYP2E1 19 and genetic polymorphisms have also been identified for this gene. 23 Because alcohol consumption is a major risk factor for OC, this SNP in ADH 3 is a prime candidate for mediating differences among individuals in OC susceptibility. Evidence of this SNPs interaction with alcohol consumption in OC risk was reported in a case control study conducted in Puerto Rico. 6 By contrast, in a study recently reported using a French population, 24 no association was found with the ADH 3 SNP but an a...