OBJECTIVES: The purpose of this study is to evaluate the pathophysiology of alcoholics by investigating the differences in frequency of Aldehyde Dehydrogenase 2(ALDH2) genotypes and ALDH2 alleles between patients with alcohol dependence and controls, and the differences of drinking and personality traits in Korean male alcoholics with ALDH2 genotype variances. METHODS: The authors selected 98 patients with alcohol dependence and 53 controls. Self-report questionnaires for acute reponses after alcohol ingestion, the AUI(Alcohol Use Inventory), and the NEO-PI-R(NEO Personality Inventory Revised) were given to all patients with alcohol dependence. ALDH2 genotypes were typed with Mbo II RFLP(Restriction Fragment Length Polymorphism) method in 53 controls and 98 patients with alcohol dependence. The authors divided alcoholic patients into two groups according to the presence of variant ALDH22 allele; normal ALDH2 alcoholics(N=87) and variant ALDH2 alcoholics(N=11). RESULTS: 1) The genotypic frequencies of subjects with ALDH21/1 were higher and those with ALDH21/2 and ALDH22/2 were lower in patients than in controls. 2) Alcohol dependence could be found in ALDH22/2 homozygote individuals. 3) Variant ALDH2 alcoholics had more family problems in the AUI than normal ALDH2 alcoholics. 4) Variant ALDH2 alcoholics experienced more flushing and cardiovascular responses after alcohol ingestion than normal ALDH2 alcoholics. 5) Variant ALDH2 alcoholics had less altruistic personality traits in the NEO-PI-R than normal ALDH2 alcoholics. 6) Variant ALDH2 alcoholics tended to have more tolerance to alcohol than normal ALDH2 alcoholics. CONCLUSION: Variant ALDH22 allele might play a protective role in the pathogenesis of alcohol dependence and there were several significant differences of drinking and personality traits in Korean male alcoholics with ALDH2 genotype variances.