Our belief that plasma proteins participate actively in the complex internal protein metabolism of the body should be adequate reason for our continued interest in blood plasma protein regeneration. It appears that the plasma can contribute protein readily to body tissues or body stores, but only in small amounts and with difficulty can the body contribute protein to the blood plasma--for example in fasting. Theterm "dynamic equilibrium" has been used to express the ebb and flow between plasma, organ, and tissue proteins. When reserve stores are exhausted the blood plasma production depends almost wholly upon food factors coming into the body from the intestine (16, 13, 9).Reserve stores under ordinary conditions are adequate to tide the body over any emergency call for new formed plasma proteins. A study of the reserve stores is in progress and it is probable that the stores of materials from which plasma proteins can be fabricated are distinct from the stores of hemoglobin building material.Infection can inhibit the formation of hemoglobin in anemia (17) and in like fashion it can inhibit the formation of plasma protein (Tables 3 and 3-a and Chart A below) during plasmapheresis. The mechanism of this interesting reaction is discussed below.