Under standardized resting conditions a given tissue eliminates a nearly constant amount of protein in its lymph per unit of time. The protein concentration in the lymph from the intestine or liver of the rat varies inversely with the volume of lymph flow. The concentrations of protein fractions in rabbit lymphs and the rates of exchange of radioiodinated human serum albumin between plasma and lymph suggest that the equilibration of plasma proteins with lymph is rapid in the liver, intermediate in the intestine, and slow in skeletal muscle.