Cell membrane damage by ultrasound was studied in human nucleated cells in vitro at various concentrations. Suspensions of human blood cells, cells of a human leukemic cell line (Reh) and mixtures of nucleated cells with erythrocytes were exposed to continuous ultrasound of 782 kHz at a SPTA intensity of 15 W/cm2. The surviving nucleated cells without membrane damage were counted on the basis of exclusion of ethidium bromide using a flow cytometer. At high cell concentrations as present in whole blood, we observed no cell death, whereas below 5 X 10(7) cells/ml most of the granulocytes, stimulated lymphocytes and Reh cells were damaged. The concentration threshold below which cells were damaged seemed not to depend on the size of the cells, rather on the concentration of particles in the suspension.
