Cholesterol and cholesterol esters have been identified on the basis of thin-layer and gas\p=m-\liquid chromatographic data and fluorimetric characteristics as major interfering fluorogens in a simple fluorimetric method for determining plasma corticosteroids.In a small series ofnormal subjects the average concentration of fluorogen, which was not 11-hydroxysteroid, was 3\m=.\4 \g=m\g.apparent cortisol/100 ml. plasma, equivalent to 22\m=.\4 % of the total fluorogen present.