Perfusion of the perilymphatic space with K+-free media leads to a gradual decline of the endocochlear potential (EP) to negative values near those observed during anoxia. The input resistance of scala media does not decrease during this time. In sharp contrast to anoxia, the ATP content of the stria vascularis (SV) remains near normal during K+-free perfusion (85%). Thus, a significant interference with strial energy generation appears unlikely. Following K+-free perfusion, the K+ content of the spiral ligament (SL) was reduced from 227 to 59 and that of the SV from 410 to 266 mmoles/kg dry wt. The pronounced reduction of the K+ content of the SL indicates that the perfusate reaches the lateral wall of the SV. These results demonstrate that a reduction of the [K+] of perilymph leads to an inhibition of the generator of the positive component of the EP. If it is true that the SV is responsible for the production of the +EP, the results suggest furthermore that K+, contained in the strial capillaries, may not have access to the generator of this potential. [Supported by NIH and NSF.]