A technique has been developed for the dissection and maintenance of coils of guinea pig cochlea in tissue culture medium in a microscope chamber where the organ of Corti is viewed with interference contrast optics. The state of the sensory cells can be judged by observing signs of degeneration such as loss of birefringence in the cell cytoplasm, appearance of the nucleus, swelling of mitochondria and cell body, and clumping of sensory hairs. A fibre of quartz-glass, 1-1.5 micron diameter, was used to probe the mechanical properties of the sensory hair bundles of outer and inner hair cells. The stereocilia were found to be laterally connected so that force applied at one point also caused movement of stereocilia at some distance from the probe. Interconnecting material was seen in the electron microscope to be present close to the tips of the stereocilia. When displaced, the stereocilia pivot at their base as stiff rods and snap back when released due to elastic properties. When overstrained, the lateral connections break and the stereocilia may fracture at the base.