1. From a consideration of previous work related to the problem of the influence of diet upon the regeneration of serum protein, a plan of study is described which eliminates the many variables shown to be operating in the studies conducted by these pioneer workers.
2. By the administration of a protein-free diet at a high level of caloric intake to the dog subjected to plasmapheresis during which one-fourth of the blood volume of the animal is withdrawn daily, it is possible to reduce the serum protein concentration to the basal level (3.5 to 4.2 per cent) and to deplete the organism of its reserve stores of this protein within 1 week. The subsequent week has been demonstrated to be an equilibrium period.
3. The dog contains a reserve store of serum protein building material equivalent to about 30 to 40 per cent of the total amount normally present in the circulation.
4. When fed the protein-free diet and when subjected to quantitative plasmapheresis, whereby the basal level of the serum protein concentration is maintained constant, the dog is able in 1 week to regenerate approximately 20 to 30 per cent of the total amount of this blood protein normally present in the plasma.
5. The administration of a diet favorable for promoting the regeneration of serum protein requires approximately 4 to 5 days before a constant and maximal response to the dietary stimulus is obtained. Equilibrium data are yielded during the 2nd week, and these are employed in calculating the potency ratio of the dietary protein.