The authors attempted to examine the allelic association between the A1 allele of Dopamine $D_2$ receptor and schizophrenia, alcoholism, drug addiction in Koreans. Schizophrenic patients(n=31), alcoholism(n=65), drug addiction(n=18) and controls(n=52) were examined by case-control study for distribution of the TaqI polymorphism of the dopamine $D_2$ receptor gene in Korean population to minimize the effect of racial differencies in gene frequencies. In schizophrenics, the numbers of schizophrenics with A1A1, A1A2, A2A2 were 9(29.0%), 15(48.4%) and 7(22.6%) respectively and in alcoholics with A1A1, A1A2, A2A2 were 14(21.5%), 36(55.4%) and 15(23.1%) respectively and in drug addiction with A1A1, A1A2, A2A2 were 2(11.1%), 10(55.6%) and 6(33.3%) respectively and in controls with A1A1, A1A2, A2A2 were 4(7.6%), 24(46.2%) and 24(46.2%) respectively. The prevalence of the A1 allele in schizophrenics, alcoholics, drug addiction and controls were 77%, 76.9%, 67% and 53.8% respectively. And the frequency of the A1 allele in schizophrenics, alcoholics, drug addiction and controls were 0.53, 0.49 0.39 and 0.31 respectively. There was significant difference in the frequency of the A1 allele between schizophrenics, alcoholics and controls. We also classified our alcoholic population. For classification by severity, we used the median MAST score 30 in our samples. There was also significant difference in the frequency of the A1 allele between less severe group(0.42) and more severe group(0.57). This data suggest that the A1 allele is associated with schizophrenia and alcoholism in Koreans. Furthermore the prevalence of the A1 allele increassed in more severely affected alcoholics. The authors conclude that our data support an allelic association between the A1 allele at dopamine $D_2$ receptor and schizophrenia, alcoholism. These results suggest the A1 allele of the $DRD_2$ gene is associated with a number of behavior disorders in which it may act as a modifying gene rather than as the primary etiological agent.