Inner ear fluids of guinea pigs and cats were analyzed for sodium, potassium, chloride, glucose, and total protein to determine species differences in chemical compositions. In the scala vestibuli perilymph and scala tympani perilymph, sodium potassium, and choride levels in the guinea pig were lower than in the cat. The protein levels in the scala vestibuli perilymph and scala tympani perilymph of the guinea pig were lower than those of the cat. The glucose levels in the guinea pig were higher in the scala vestibuli perilymph and scala tympani perilymph, as compared to findings in the cat. Regarding the utricular endolymph, there were significant differences between guinea pigs and cats in sodium and potassium concentrations; the concentration in the former being higher in sodium and lower in potassium. These findings are pertinent for the phylogenetic studies on inner ear fluid biochemistry.