Two enzymatic methods for the determination of cholesterol in serum have been modified for automatic use. These methods utilize the colour reactions according to Kageyama or Trinder to measure the hydrogen peroxide resulting from the enzymatic reaction. The procedures have been compared with the classical methods according to Abell and to Huang. Details regarding the procedures are given. Comparisons made during routine analysis of a large number of different sera have been expressed in the form of regression equations. The standard errors of the methods are given along with the standard deviations for differences between methods. Some conversions of values from one method into another are also given. It appears that the automated Kageyama method can be used for large scale practice. The manual Kageyama method is not very satisfactory because of its large experimental error. A disadvantage of the Kageyama methods is the necessity of having blank corrections for haemolytic sera. The Trinder method avoids the problem and has some additional advantages.