In a preceding publication (1) evidence was presented to show that surviving liver cells in the presence of oxygen produce urea and lose water, whereas with anoxia little, if any, urea is formed and water enters the ceils in considerable quantity. I t seemed probable that intracellular amino acids and substances derived from them-for example, arginine, ornithine and citrulline-can maintain a high intraceilular osmotic pressure but with formation of urea, leave the ceils. Kidney cells which form little, if any, urea undergo swelling both in the presence and absence of oxygen.The purpose of the present study has been to determine how a varied supply of oxygen influences the movement of water in surviving fiver tissue. The a t t e m p t has been made to imitate in vitro as closely as possible conditions present during life.