This study investigated whether acid invertase activities correlate with glucose contents in tubers of eight cultivars under commercial storage conditions at 7°C and during subsequent reconditioning (21°C, 3 weeks). Both basal activity (from invertase without removing its naturally bound inhibitors) and total activity (from invertase after removing inhibitors by vortexing) were measured for acid invertase. The basal and total acid invertase activities, and glucose contents of all eight cultivars increased during 7°C storage and decreased during reconditioning. The basal activity of acid invertase showed a stronger correlation to glucose content than did the total activity of acid invertase. Low (relatively) sugar cultivars (Atlantic, F88007, ND860-2, Snowden) had lower basal activities than did high sugar cultivars. Basal activity of 'Atlantic' was relatively low but total activity was the lowest among all cultivars, which indicated a relatively weak inhibition; 'ND860-2, showed both the lowest basal activity and a low total activity. 'Snowden' exhibited the strongest inhibitions (86% reduction) and the second lowest basal activity although the total activity was among the highest. The results suggest that low sugar content may result from either low total activity or strong inhibition as long as the basal activity of acid invertase is low.