An ultrasound contrast agent composed of at least one kind of low-boiling water-insoluble substance (with a boiling point lower than 37° C.) and at least one kind of high-boiling water-insoluble substance (with a boiling point higher than 37° C.). The former vaporizes to absorb ultrasonic energy upon application of ultrasound, thereby causing the latter to vaporize secondarily, with the resulting bubbles producing an echo image. It is less liable to bumping and hence safe.
