Methods were selected and tested for studying the flux of water through the labyrinthine walls. Mannitol which does not pass through the walls was used in isotonic concentration in the endolymphatic space, and various concentrations of mannitol solutions in the perilymph space created a concentration gradient which resulted in a flux of water through the membranous wall. This is a first step in investigating the flux of solutes and solvent through these walls of the labyrinth as a basis for studying substances which chronically increase the colloid osmotic pressure due to their difficulty in passing the walls.