Ultrasonic irradiation of mammalian cells in vitro at hyperthermic temperatures

Suspensions of V79 cells and HeLa cells have been irradiated with continuous 3 MHz ultrasound at a spatial average intensity of 3W cm-2. This irradiation condition did not give rise to cell lysis. When the cells were irradiated with ultrasound for up to six hours at 37 degrees C no cell killing was observed. However, at temperatures in the hyperthermia range 42--45 degrees C the increase in cell killing that resulted from the irradiation was greater than that which could be attributed to its heating effect alone.