Abstract Changes in acid content in fruits of tomato ( Lycopersicon esculentum Mill.) left on the vine compared with those of fruits removed from the vine at one stage each of development and ripening. Developing fruits detached 28 days after anthesis had an increase in total acidity attributable to increased malic and citric acid concentrations. Detached developing fruits accumulated organic acids more rapidly than attached fruits. Mature fruits detached at the breaker stage decreased more in total acidity than attached fruits which was reflected in a decrease in malic and citric acids, with a greater decrease in malic acid. The data indicate that organic acid accumulation in detached fruits is determined by metabolism at the time of detachment.