β 1 -and β 2 -Adrenergic receptors (β 1 -AR and β 2 -AR) are co-expressed in numerous tissues, for example, heart and bladder. They play a very important role in the responses of a variety of organs to sympathetic nerve stimulation. Recent studies suggest that many G protein-coupled receptors, such as β 1 -AR, β 2 -AR, μ opioid receptor and δ opioid receptor, can form homo-and heterooligomers. Previous studies demonstrated that the β 1 -AR and β 2 -AR formed dimers in living HEK 293 cells. The aim of the present study is to investigate whether such heterooligomerization affect the agonist-induced receptor internalization in the CHO-K1 cells stably co-expressing β 1 -AR and β 2 -AR. Using co-immunoprecipitation, we confirmed that β 1 -AR and β 2 -AR formed heterooligomers in the CHO-K1 cells. In cells co-expressing β 1 -AR and β 2 -AR, 30% of β 1 -AR was internalized by isoproterenol, whereas only 20% of β 1 -AR was internalized in cells expressing the β 1 -AR alone. Heterooligomerization did not affect the ratio of internalized β 2 -AR. Salmeterol, a specific β 2 -AR agonist, broke β 1 -AR/β 2 -AR heterooligomers, and induced β 2 -AR-specific internalization in cells co-expressing β 1 -AR and β 2 -AR. The present study demonstrated that heterooligomerization between β 1 -AR and β 2 -AR accelerates the isoproterenol-promoted internalization of the β 1 -AR, and that salmeterol induces β 2 -AR-specific internalization in Chinese hamster ovary (CHO) cells stably co-expressing β 1 -AR and β 2 -AR.