Reserpine (2 mg/kg and 10 mg/kg, i.p.), an adrenergic blocker, was administered to normal guinea pigs, and samples of serum, CSF, scala tympani perilymph, scala vestibuli perilymph and cochlear endolymph were collected. The concentrations of Na and K in these fluids were then assessed to observe electrolyte distributions. Both Na and K concentrations were reduced in serum. In CSF, the Na concentration was markedly depressed, while the K concentration remained unchanged. Scala tympani perilymph showed a pattern of electrolyte changes similar to that in CSF. In scala vestibuli perilymph, the Na concentration was unaltered, but the K concentration was lowered. Cochlear endolymph exhibited no change of the Na concentration but there was a marked decrease in the K concentration. These changes are thought to be attributable to the indirect blockage of energy producing systems in membrane transport in the inner ear by the reserpine-induced depletion of catecholamines.