The multiplicity of tyrosine hydroxylase (TH) mRNA was examined in two species of primate, Macaca irus and Macaca fuscata, one species of insectivore, Sunkus murinus and one species of rodent, rat. To investigate the TH multiplicity, total RNAs from various species of animals were reverse transcribed and 5' portion of TH cDNAs were amplified by polymerase chain reaction. The resulted DNA fragments were analyzed by agarose gel electrophoresis. Two types of TH mRNA corresponding to type 1 and type 2 were detected in adrenal gland and brain of both species of primate. In contrast, only a single form of TH mRNA was detected in Sunkus murinus and rat.