The invention disclosed herein relates to a method of cavitation-induced delivery of a therapeutic or diagnostic agent to a human or animal subject. In particular the invention provides an agent for use in a method of diagnosis or treatment of a human or animal subject, the method comprising exposing the subject to ultrasound, wherein the agent comprises a therapeutic or diagnostic component which is covalently bound to a dense component, the dense component having a density greater than that of the therapeutic or diagnostic component, and wherein either the dense component is a cavitation initiator or the method comprises administering to the subject a further agent which is a cavitation initiator. Binding of the dense component enhances cavitation-induced transport of the therapeutic or diagnostic component.
