Sucrose breakdown in mature acidic ;Persian' limes (Citrus aurantifolia [Christm.] Swing.) occurred at a rate of 30.6 picomoles per milliliter per day during 9 weeks storage at 15 degrees C. Neither enzyme of sucrose catabolism (sucrose synthase or acid/alkaline invertase) was present in extracts of mature storage tissue. The average vacuolar pH, estimated by direct measurement of sap from isolated vacuoles and by the methylamine method, was about 2.0 to 2.2. In vitro acid hydrolysis of sucrose at physiological concentrations in a buffered solution (pH 2.2) occurred at identical rates as in matured limes. The results indicate that sucrose breakdown in stored mature acidic limes occurs by acid hydrolysis.