**6. Concluding remarks**

Much exciting work on ultrasound-mediated gene delivery has already been done, but the field remains young and even preclinical applications involving therapeutic genes are relatively few. A few generalities may be put forth: In most (but not all) cases, ultrasoundmediated gene delivery is dependent on, or greatly facilitated by, exogenous microbubbles. Where this is the case, the acoustic exposures are usually such that the bubbles can be expected to behave in a nonlinear way. Given the intense effort being devoted to the topic, we can anticipate with some confidence that successful gene therapies in large animals and early human trials will be achieved in the near future.
