The D1 and D2 dopamine receptors have been biochemically characterized using specific probes based on the subtype selective antagonists SCH 23390 and spiperone, respectively. The D2 dopamine receptor was identified from several tissues by photoaffinity labeling and was purified from bovine anterior pituitary to homogeneity using a combination of affinity, lectin and hydroxylapatite chromatography. A complementary DNA (cDNA) encoding a rat brain D2 dopamine receptor has been cloned via low stringency hybridization using a portion of the beta 2-adrenergic receptor gene as a probe. Photoaffinity crosslinking and affinity chromatography have also been used to identify and purify the rat brain D1 dopamine receptor.