The clinical utility of ultrasound contrast agents has been established in diagnostic echocardiography. Recently, the use of such agents has been promoted for transport and delivery of various bioactive substances, thus providing a technique for non-invasive gene therapy and organ-specific drug delivery. In this review, we give a critical update of published studies using ultrasound contrast agents for therapeutic use. We discuss the potential applicationsandlimitationsofthistechniqueandsuggestfutureapplicationsincardiovascular medicine. (J Am Coll Cardiol 2005;45:329–35) © 2005 by the American College of Cardiology Foundation