Mammalian cochlea perilymph contains amino acids and protein which have a major effect on the electrochemistry of an implanted auditory prosthesis. Cyclic voltammetry in an artificial perilymph solution shows that many amino acids adsorb at the platinum electrode diminishing oxidation of the metal, and also blocking hydrogen evolution. At anodic potentials > 900 mV vs. silver/silver chloride they are oxidized leaving adsorbed oxidation products. The sulfur-containing amino acids cysteine and methionine have the greatest effects. Protein (human serum albumen, HSA) has a similar hat smaller effect. A solution containing HSA (2 mg mL(-1)), phenylalanine (175 muM), glycine (396 muM), and proline (40 muM) in phosphate buffered saline is proposed as a suitable artificial perilymph solution having similar electrochemical and adsorption properties to perilymph. (C) 2000 The Electrochemical Society. S0013-4651(99)12-019-4. All rights reserved.