Abstract: The invention provides a method of sensitizing target cells to ultrasound energy using a stimulus such as an electric field. This “electrosensitisation” enables target cells to be disrupted by ultrasound at frequencies and energies of ultrasound which do not cause disruption of non-sensitized (i.e., non-target) cells. As a consequence, the method increases the selectivity of ultrasound therapy, providing a way to ablate undesired cells, such as diseased cells (e.g., tumor cells) while minimizing harm to neighboring cells. In another aspect, however, ultrasound can be used to sensitize cells while the electrical field is used to disrupt cells. The invention also provides an apparatus for performing the method and assays for identifying gene products and other molecules involved in apoptosis.