Two parts of the dopamine beta-hydroxylase (DBH) gene, one a 7.5-kb single copy fragment (F1) spanning the 5'-flanking region to exon 3 and the second a 9.0-kb single copy fragment (F2) spanning exon 3 to exon 7, were amplified by a long PCR procedure in 161 unrelated patients with schizophrenia and 67 unrelated control subjects. The PCR products were completely digested with the restriction enzyme TaqI. These subjects were classified into genetic subgroups according to the TaqI restriction fragment length polymorphisms (RFLPs) for the human DBH gene, and the association of the TaqI RFLPs with biochemical alterations of the catecholamine pathway in schizophrenia was then examined. The frequencies of the two TaqI polymorphic sites did not show significant differences between the patients and control subjects, but the TaqI RFLPs were found to be associated with biochemical alterations of the catecholamine pathway in schizophrenia.