Cerebrospinal fluid, perilymph and endolymph of the saccule, the utricle and the semicircular duct of the trout were prepared from frozen inner ears. Blood was collected after the decapitation of the animal. In all samples of each animal the concentrations of sodium, potassium, protein and glucose were determined. The electrolyte values and the total protein content were used to estimate the purity of a sample. The concentration of sodium is high in perilymph and low in endolymph whereas potassium is high in endolymph and low in perilymph. The differences between perilymph and the cerebrospinal fluid as well as the blood serum are significant. A relative independent production of the inner ear fluids can be assumed.