The conc. of cholesterol in the blood serum did not change significantly in normal, spayed,-or hypothyroid monkeys during the 8 hrs. following the ingestion of several eggs, nor was there any post-absorptive change 24 hrs. later. However, when egg feeding was continued for 4 days, a definite rise was usually evident on the 2d day and a maximum, averaging more than 50% above the starting value, was reached usually on the day after egg feeding was stopped. Both combined and free cholesterol increased the combined fraction proportionately more than the free. No rise in cholesterol conc. followed the adm. for 4 days of an amt. of cholesterol, approx. equivalent to that ingested in the eggs, in the form of an emulsion. This result was not entirely conclusive because of some vomiting. A slight rise in cholesterol conc. somewhat smaller than that which followed egg feeding, occurred after the same amt. of cholesterol had been given for 4 days in oil soln. About half as large an increase was found when the same amt. of oil was given under the same conditions to the same monkeys. Adm. of egg phosphatides for 4 days did not cause any increase in serum cholesterol conc. Evidence was obtained indicating that the proportion between the cholesterol fractions of the blood serum is not controlled in the monkey with the rigidity which characterizes the human being. No evidence for a latent disturbance in cholesterol metabolism in hypothyroid monkeya was obtained; in none of the expts., with 1 possible exception, did thyroidectomized animals respond in a manner different from that manifested by normal and spayed monkeys.