In order to clone the third subtype of human alpha-2 adrenergic receptor, polymerase chain reaction (PCR) was employed. Primer pairs corresponding to the conserved sequences in transmembrane domains III and VI were used to selectively amplify the adrenergic receptor genes of the alpha-2 type from human genomic DNA. Sequence data obtained from a clone PCRA2, 885 bps in length, revealed the presence of significant (80%) homology with the known alpha-2A and 2B subtypes of human in the transmembrane domains, whereas distinct variations were noted in the third cytoplasmic loop. When compared with a recently reported alpha-2 receptor gene of rat, essentially identical sequences were found in the transmembrane domains III-VI, except one amino acid in domain VI. As high as 65% homology was also found in the third cytoplasmic loop. We suggest this in vitro amplified fragment represents the partial gene of the third subtype of alpha-2 adrenergic receptor in human.