We studied the relationship between schizophrenia and the DdeI polymorphism in the 5' untranslated region (5'UTR) of the dopamine D1 receptor (DRD1) gene. This polymorphism is an A (A1 allele) to G (A2 allele) transition in the 5' UTR of exon 2 at bp -48 (A-48G). One hundred forty-eight schizophrenics and 148 control subjects were investigated. No significant differences in genotypic counts and allele frequencies between schizophrenics and controls were found. Although a significant difference between the patients classified as disorganized type and the controls was discovered both in genotypic counts and allele frequencies, neither association proved significant when a Bonferroni correction was used. Moreover, there were no differences in scores of main symptoms of schizophrenia based on the Manchester Scale between patients with A1/A1 genotype and those with A1/A2 genotype. These findings suggest that this gene may not be involved in the pathogenesis of schizophrenia.