Naturally‐isolated living cells were subjected to ultrasonic vibration by means of the tip of a steel needle applied directly to the cell surface or inserted into a drop of a suspension of cells in sea water. The needle was machined into the tip of a stainless‐steel cone, and the base of the cone was glued to one end of an electroded and polarized barium titanate hollow cylinder. This composite transducer was driven at its resonant frequency of approximately 85 000 cps. Ultrasound applier to the surfaces of egg cells of marine invertebrates produces rotation, translation, deformation, and fragmentation of the nucleoli; rotation and deformation of the nuclei; acoustic streaming of nucleoplasm and cytoplasm; and deformation of the cellular surface and fragmentation of the cell. Cells and intracellular bodies are often attracted to the sound source as a result of acoustic‐radiation pressure, and, especially for whole cells in suspension, this attractive tendency is typically superposed on a tendency of the body to take part in acoustic streaming of the surrounding medium. Some aspects of the motion can be accounted for in terms of presently available theory of nonlinear acoustics. Information on the physical properties of nucleolus, nucleoplasm, and cytoplasm is gained from use of this sonic technique.