Abstract A direct method for the quantitative determination of total serum cholesterol is described. The procedure consists of adding a reagent containing sulfuric acid, acetic acid, and ferric chloride to a 0.1 ml. sample of serum. The sensitivity achieved is several times that of current procedures and the time required for a single determination is in the order of minutes. Precision and reproducibility are demonstrated as well as the absorption characteristics of the purple color produced through the spectral range of 400 to 700 mμ. Finally, the method is compared with samples in which total cholesterol is determined by the Kingsley-Schaffert and Schoenheimer-Sperry procedures.