The rat tyrosine hydroxylase gene (TH) from a panel of outbred and inbred rat strains has been analysed by Southern blotting, restriction-endonuclease mapping and direct sequencing of PCR-amplified products for detecting DNA polymorphisms. Five polymorphic sites have been characterized. This information may be used in pharmacogenetic studies to determine the influence of the TH gene in animal models of affective disorders and addictive behaviours.