We studied the allelic distributions of 48-base pair repeat polymorphism of the dopamine D4 receptor (DRD4) gene in two groups of schizophrenic patients, one with any schizophrenic member in the family (L(+) group) and the other without schizophrenic family histories (L(-) group), and healthy controls. The frequency of the sum of the alleles of 4, 5, and 6 repeats in the L(+) group was significantly higher than the controls. The frequency of the allele of 4 repeats in the L(-) group was significantly higher than the controls. These results show positive allelic associations between DRD4 polymorphism and each of the two groups of schizophrenic patients.