Pathogenesis of inner ear deafness are thought to be due largely to imbalance of potassium and sodium ions in the inner ear fluids. Such imbalance can occur with renal diseases, vascular insufficiencies, and ototoxic drugs. An ion‐specific micro‐electrode was applied to the peri‐ or endo‐lymph in chinchilla's cochlea. Simultaneous measurements of endocochlear dc potentials (EP) and K‐ion concentration were made over a period of a few hours and their changes following temporary asphyxia, following various loop diuretics, following permanent anoxia were studied. The reduction of endolymph potassium concentration was accompanied by the elevation of perilymph concentration of this cation following loop diuretics. Normal values for K+in the inner ear fluids and potassium conductance following various doses of loop diuretics will be discussed in detail.