A survey of a number of methods for the determination of the diacetyl content of beer resulted in the recommendation for routine use of a colorimetric technique based on the method of Owades, Jakovac & Vigilante. The method is both simple and rapid in operation but is not specific for diacetyl, estimating also other related diketones. It was felt, however, that the estimation of vicinal diketones was advantageous since the results were more in line with aroma assessment. The Analysis Committee appointed the following Sub-Committee to recommend a method for the determination of diacetyl in beer:– R. G. Ault (Chairman), M. O. Jones, J. R. Hudson, G. A. Howard, P. A. Martin P. F. Bayles, L. R. Bishop, R. N. Greenshields, L. Taylor, A. Sinclair (co-opted). The findings of the Sub-Committee are given in this paper.