Young guinea pigs (250-300 g) were rapidly decapitated and the temporal bones were immediately removed. Under dissecting microscope, the crista ampullaris was removed and incubated in Hank's balanced salt solution containing 0.125 mg/ml collagenase (Sigma IV) at 37 degrees C for 50-60 min. After mechanical dissociation, the isolated cells were transferred onto the coverslips coated with poly-lysine. The cells were left 10-15 min to settle down on the coverslips. Afterward, the collagenase containing solution was replaced by Hank's solution. Observations were made under converted phase-contrast microscope. The results were as follows: 1. Vestibular hair cells are classified into two types. Type I cell was flask-shaped with sensory hairs, a cuticular plate, a long neck and a round bottom containing a large nucleus. The length of type I cell was 18.10 +/- 2.05 microns (mean +/- s n = 32). Type II cells were round shaped or cylindrically shaped without neck but with sensory hairs, a cuticular plate. The longitudinal axis of cylindrically shaped cell was 14.00 +/- 3.16 microns and horizontal axis 9.88 +/- 2.01 microns (mean +/- s n = 29). The diameter of the round cell was 10.31 +/- 1.98 microns (mean +/- s n = 10). 2. The proportion of type I and type II cells was 61/39. 3. An average of 500-700 vestibular hair cells were obtained from each ampulla. 4. Generally, vestibular hair cells could live in Hank's solution for 7-8 hours. The earliest sign of viability degression was the appearance of granules in the cytoplasm.