A cDNA clone, which has an open reading frame of 1398 nucleotides encoding a 466-amino-acid peptide, has been isolated from rabbit liver cDNA library. Compared with the peptide sequence, it shows high homology to alpha1a adrenoceptors of human, bovine and rat. We expressed this clone in COS-7 and investigated the pharmacological properties, revealing similarity to those of human alpha1a adrenoceptors. Competitive RT/PCR has detected the mRNA in variety of rabbit tissues, especially abundantly in liver, vas deferens, brain, and aorta, but not in heart.