The effect of 1-MHz cw ultrasound (0.36 MPa in pressure amplitude) on cell detachment and gene transfection in adherent HeLa cells was investigated. Cell detachment, cell injury, and gene transfection (up to 50%) in surviving populations were found to increase progressively with exposure duration (0-20 s). However, with respect to the total exposed cells, gene transfection efficiency in the adherent cells (3%) was significantly lower than its counterpart without detachment (15%). Cell detachment by ultrasound exposure was accompanied by significantly reduced proliferation rate with greatly increased apoptosis in the surviving detached cell population. © 2005 Acoustical Society of America.