Alpha1A-adrenoceptors are important regulators of prostatic smooth muscle tone and an important target for therapy of lower urinary tract symptoms. The function of heptahelical transmembrane receptors such as adrenoceptors can be regulated by β-arrestin-2, which may bind to receptors besides G proteins. Here, we investigated the expression and α1A-adrenoceptor binding of β-arrestin-2 in the human prostate.Human prostatic tissues were obtained from patients undergoing radical prostatectomies. The expression of β-arrestin-2 and α1A-adrenoceptors was studied by RT-PCR, Western blot analysis, and immunohistochemistry. The protein-protein interaction between α1A-adrenoceptors and β-arrestin-2 was investigated by coimmunoprecipitation.RT-PCR and Western blot analysis demonstrated the expression of β-arrestin-2 mRNA and protein in the human prostate. Immunohistochemistry demonstrated β-arrestin-2 expression in smooth muscle and stromal cells. Coimmunoprecipitation studies demonstrated that α1A-adrenoceptors in the human prostate may interact with β-arrestin-2. Thus, specific binding of β-arrestin-2 to α1A-adrenoceptors was significantly higher than background during α1A-adrenoceptor detection in β-arrestin-2 precipitates (P < 0.001) or during β-arrestin-2 detection in α1A-adrenoceptor precipitates (P < 0.005). This interaction may be located to prostate smooth muscle cells, as expression of the α1A-adrenoceptor was exclusively found in smooth muscle cells after immunohistochemical staining.With β-arrestin-2, we identified a new binding partner of the α1A-adrenoceptor in human prostate smooth muscle. Binding of β-arrestin-2 may be involved in posttranslational regulation of prostate α1A-adrenoceptors.