Ultrasound contrast agents (microbubbles) lower the threshold for cavitation by ultrasound energy. Ultrasound microbubbles may be used as cavitation nuclei for drug and gene delivery. By tailoring the physical properties of microbubbles and coating materials, drugs and genetic drugs can be incorporated into ultrasound contrast agents. As the microbubbles enter the region of insonation, the microbubbles cavitate, locally releasing the therapeutic agents. Cavitation also causes a local shockwave that improves cellular uptake of the therapeutic agent. As a result of the human genome project and continuing advances in molecular biology, many therapeutic genes have been discovered. In the cardiovascular system, gene therapy has the potential to improve myocardial vascularization and ameliorate congestive heart failure. For successful development of clinical gene therapy, however, effective gene delivery vectors are needed. Ultrasound contrast agents can be used to develop new, more effective vectors for gene delivery. Transthoracic ultrasound can be focused on the heart so that an intravenous injection of gene-bearing microbubbles will deliver genes relatively selectively to the myocardium. Using this technique, we have produced high levels of transgene expression in the insonated region of the myocardium. This new technology, using microbubbles and ultrasound for drug and gene delivery, merits further study and development.