The Na+ concentration in saccular endolymph in guinea pigs was measured and found to be 3.2±0.6 mEqu/l with sodium specific electrodes. The saccular potential varied between −8 and +2.4 mV. Permanent anoxia resulting in the death of the animal caused the potential to fall by 15 mV and the Na+ concentration to rise to 40 mEqu/l in 30 min. Maintenance of the Na+ concentration in saccular endolymph and the saccular potential depended upon the integrity of the first turn of the cochlea. The access resistance of the saccule was measured and found to be 16 kohms and the resistance of the ductus reuniens calculated to be 181 kohms. It was concluded that the saccule derives its endolymph and potential from the cochlea via the ductus reuniens.