This paper will focus on physiological evidence for a lymph node concentrating-diluting mechanism. The mechanism is based on the finding that the protein concentration of efferent lymph leaving the node will change in the direction required to establish equilibrium of the Starling forces acting across the blood-lymph barrier of the lymph node. Therefore, the lymph proteins may become concentrated or diluted during nodal transit, depending on the direction of net fluid transfer between the lymph and blood vascular compartments; if the Starling forces are balanced perfectly, the lymph will not be altered.