A rapid method for the colorimetric analysis of micro quantities, of citric acid beginning at concentrations of 0·01% of citric acid in milk and in dairy products has been described. The analysis is based on the yellow colour which develops upon reacting citric acid with pyridine in a solution of acetic anhydride, as applied by Saffran & Denstedt for the estimation of citric acid in blood. The accuracy of the method in the ranges normally used in the estimation of citric acid in milk is approximately ±3%. Examples of determinations in milk and dairy products are given.