Recent human genetic studies suggest that a predisposition to alcohol abuse and/or to develop alcoholism may be inherited. Pedigree analysis, linkage, and association studies have helped to detect marker loci and candidate genes that may prove useful in identifying individuals at risk. In particular, molecular genetic research into the causes of alcoholism has drawn attention to the potentially important role of alcohol-and acetaldehyde-metabolizing enzymes, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Functional polymorphisms have been observed at various genes encoding these enzyme proteins, all of which act to alter the rate of synthesis of the toxic metabolite acetaldehyde, or decrease its further oxidation. The occurrence of functional polymorphisms in alcohol-metabolizing enzymes makes them favored candidate genes suitable for further molecular genetic research. A positive selection of such genetic polymorphisms in some populations might act as a protective factor against alcohol abuse and alcohol-related disease outcomes. For example, individuals who show initial sensitivity to alcohol by virtue of their genetically controlled abnormality of ALDH2*2 allele are discouraged from excessive alcohol consumption. On the other hand, persons with the heterozygous ALDH2*2 genotype (ALDH2*1/2*2) are at higher risk for developing alcohol abuse-related end-organ damage than those with a homozygous ALDH2* 1/2*1 genotype. Moreover, the frequency of c2 allele of cytochrome P45 02E1 was found to be higher in patients with nonfibrotic alcoholic liver disease than in patients with severe hepatic fibrosis or liver cirrhosis. Identification of putative alcoholism vulnerability genes by direct analysis of candidate genes and genetic linkage may therefore help improve approaches to prevention and treatment.