The Na+ concentration in utricular endolymph of guinea pigs was measured with Na+ specific electrodes and found to be 12.6±5.8 mEqu/l. The utricular potential was 1.8±4.4 mV. Permanent anoxia resulting in the death of the animal caused the potential to fall by 15 mV and the Na+ concentration to rise at a rate of 0.4 mEqu/l per minute. The utricular potential could be maintained during anoxia by bubbling the surrounding perilymph with air or oxygen. Maintenance of the Na+ concentration and the utricular potential did not depend on the integrity of the first turn of the cochlea. It was concluded that the utricle produced its own endolymph and potential and was effectively isolated from the cochlea. The access resistance of the utricle was measured to be 2±1.1 kohms.