The investigation described in this paper1 represents part of a comprehensive study of the cholesterol in the blood of normal and diseased human subjects. Although the field has been studied extensively by many workers in the past, I felt justified in undertaking such a study for the following reasons:
1. There are wide differences in the normal values for total cholesterol of the serum reported by different authors, the range between minimum and maximum average values amounting to almost 100 per cent of the minimum.2 The inconsistent results are due, in considerable part, to the use of inaccurate methods. The frequent publication of new procedures for the determination of cholesterol indicates that none has been found to be entirely satisfactory. Recently Schoenheimer and I3 described a method which permits the rapid determination of total and free cholesterol with satisfactory accuracy in 0.2 cc. of serum or plasma.