Abscission zone tissue of citrus was shown to have a higher rate of protein synthesis than tissue distal or proximal to it, based on the incorporation of leucine-1-(14)C. The proximal tissue had the slowest rate of protein synthesis. As the tissue approached abscission, the rate of synthesis in the abscission zone decreased and the differences in rate of protein synthesis between the 3 zones almost disappeared. IAA, which delayed abscission, maintained the protein synthesis gradient between the abscission and proximal zones, but the distal zone tissue was as active in protein synthesis as the abscission zone. Differences in uptake of the leucine were also observed between different zones and treatments. Regardless of the tissue or the treatment, there was a sharp increase in uptake at the 24 hour point.Direct incubation of abscission zones in IAA and gibberellic acid (GA) indicated that the action of gibberellic acid on abscission is probably through a stimulation of protein synthesis, while IAA seems to act by maintaining the existing rate of protein synthesis in the cells of the abscission zone.