THE importance of the dopaminergic system in brain function has been emphasized by its association with neurological and psychiatric disorders such as Parkinson's disease and schizophrenia. On the basis of their biochemical and pharmacological characteristics, dopamine receptors are classified into D1 and D2 subtypes1,2. As the most abundant dopamine receptor in the central nervous system, D1 receptors seem to mediate some behavioural responses3, modulate activity of D2 dopamine receptors4,5, and regulate neuron growth and differentiation6. The D2 dopamine receptor has been cloned by low-stringency screening7. We report here the cloning of human and rat D1 dopamine receptors by applying an approach based on the polymerase chain reaction8. The cloned human D1 dopamine receptor has been characterized on the basis of four criteria: the deduced amino-acid sequence, which reveals that it is a G protein-coupled receptor; the tissue distribution of its messenger RNA, which is compatible with that of the Dl dopamine receptor; its pharmacological profile when transfected into COS-7 cells; and its ability to stimulate the accumulation of cyclic AMP in human 293 cells.