We have developed an online analytical method that combines alpha(1A)-adrenoceptor (alpha(1A)AR) cell membrane chromatography (alpha(1A)AR-CMC) with high performance liquid chromatography and mass spectrometry (HPLC/MS) for the identification of active components from Radix Caulophylli acting on the human alpha(1A)AR. Fractions retained by the alpha(1A)AR-CMC column were captured into a loop and the components were directly analyzed by combining an 8 port column switcher with an HPLC/MS system for separation and preliminary identification. Using methoxamine as a positive control drug, magnoflorine and caulophine from Radix Caulophylli were identified as the active molecules acting on the alpha(1A)AR. This new alpha(1A)AR-CMC-online-HPLC/MS method can be applied for screening active components acting on alpha(1A)AR from traditional Chinese medicines exemplified by Radix Caulophylli. This method will be of great utility in drug discovery using natural medicinal herbs as a source of novel compounds.