Adrenergic receptors are pharmacologically classified into the receptor types alpha(1), alpha(2), beta(1), beta(2), and beta(3). Structural differences and varying affinities in radioligand binding studies lead to a further classification of alpha(1)- and alpha(2)-receptors into subtypes which are termed alpha(1A) (formerly alpha(1C)), alpha(1B), and alpha(1D) (formerly alpha(1AD)), and alpha(2AD), alpha(2B), and alpha(2C), respectively. mRNA expression of all but one alpha-adrenergic receptor subtypes and of all beta-adrenergic receptor types was measured quantitatively in total RNA extracted from mammary tissue of 10 lactating dairy cows by real-time reverse transcription (RT) polymerase chain reaction (PCR). mRNA expression of alpha(1)-adrenergic receptors was highest for the alpha(1A)-subtype followed by alpha(1B), whereas the alpha(1D)-subtype could not be detected. The highest mRNA expression of alpha(2)-adrenergic receptors was found for the alpha(2AD)-subtype, followed by alpha(2B) and alpha(2C). Within the beta-adrenergic receptors, the beta(2)-receptor type was most highly expressed, followed by beta(1) and beta(3). In conclusion, eight of nine adrenergic receptors classified to date were detected and relatively quantified in the mammary gland of dairy cows.