Dopamine (DA) is a major central nervous system (CNS) neurotransmitter with many important physiological activities. Investigations into the neuroanatomy and neurologic functions of the dopaminergic neural systems have generated much debate. Regarding neuroanatomy, physiological and pharmacological criteria have divided DA receptors into D1 and D2 subtypes. The genes encoding these subtypes have been cloned and classified into a D1 subfamily encompassing D1 and D5 receptors and a D2 subfamily with D2, D3, and D4. Based on the sequences of the cloned receptors, we prepared antibodies and riboprobes to elucidate the expression of the corresponding proteins and mRNAs in the rat area postrema (AP) by immunohistochemistry and in situ hybridization (ISH). The AP was obtained from adult male Sprague-Dawley rats undergoing brain surgery, and tissue samples were used for RT-PCR, immunohistochemistry, and ISH. The results showed that D2 and D5 receptors and their mRNAs exist in the rat AP. On the other hand, D1, D3, and D4 receptors and their mRNAs were not detected.