Microbubbles, currently used as contrast agents have potential therapeutic applications. Microbubbles, upon insonation of sufficiently intense ultrasound will cavitate. Cavitation with microbubbles can be used to dissolve blood clots or deliver drugs. Targeting ligands and drugs can be incorporated into microbubbles to make highly specific diagnostic and therapeutic agents for activation with ultrasound. In this paper I will review some of these potential applications and experimental results using such agents for thrombolysis, drug and gene delivery.