Four studies on variants of the D2 receptor gene (Ser→Cys), Bal 1 polymorphism in D3, 48-nucleotide repeat polymorphism in D4, and 40-nucleotide repeat polymorphism in the dopamine transporter gene were carried out in patients with schizophrenia (n＝73), mood disorder (n＝11), neurological disease (n＝41) and controls (n＝29). Each polymorphism was typed by amplification of genomic DNA by PCR and agarose gel electrophoresis. Eight individuals were heterozygous for Cys/Ser 311 of D2 and three of these eight were schizophrenia patients and two of the three had family histories of the illness. Two patients with schizophrenia were homozygous for the mutant form of D3 and showed a stuporous state at disease onset. It was detected that four-fold and two-fold repeats in D4, and ten-fold, nine-fold and seven-fold repeats in the dopamine transporter gene. There was no evidence of association between any of these variants and reactivity to pharmacotherapy for schizophrenia.