1. The range of free cholesterol in the blood of rabbits, as determined by the Windaus method, varies from 35 to 125 mg. with a mean of 71 mg. per 100 cc. of blood.
2. The small amount of cholesterol contained in the high protein diet used by us in earlier work and causing atherosclerosis does not affect the blood cholesterol nor does it cause arterial disease.
3. In order to produce atherosclerosis it is necessary to feed at least ten times that amount of cholesterol.
4. In rabbits receiving such amounts both hypercholesterolemia and atherosclerosis occur, but it is not possible to establish any close parallelism between the two. High blood readings are found in rabbits with normal aortæ and atherosclerotic rabbits in this series sometimes have shown a normal blood cholesterol.
5. With still greater doses of cholesterol one finally reaches an amount which regularly produces hypercholesterolemia and atherosclerosis within a few weeks.
6. A new series of rabbits fed the high protein diet shows that those rabbits which become atherosclerotic also develop hypercholesterolemia. We attribute this elevation of the blood cholesterol to a metabolic disturbance directly referable to the excess of protein in the diet and not to its cholesterol content.