Abstract: Physiological function-enhancing agents to be used for the treatment of tumors comprise a compound capable of stimulating the generation of at least one type of active oxygen, such as superoxide radicals and singlet oxygen, upon ultrasonic irradiation (e.g., porphyrins, chlorins, methylene-blue, fluorescein, acridine derivatives, rhodamines and tetracyclines).Irradiating ultrasonic waves onto tumor tissues, with this agent orally or parenterally administered in advance, causes the active ingredient present at the irradiated site to generate active oxygen (e.g., superoxide radicals and singlet oxygen), which serves to destruct the tumor cells.These agents are very low in toxicity and exhibit antitumor activity only upon ultrasonic irradiation. Hence, there is no risk of causing any systemic idsorder. In addition, these act exclusively upon tumor tissues when combined with ultrasonic irradiation, with no adverse effect upon normal tissues.