The possibility that leaf abscission might involve a mobilization phenomenon leading to a localized cellular senescence was examined by following dry weight changes, chlorophyll content, and protein levels in proximal and distal tissue of excised pieces of bean petioles from Phaseolus vulgaris L. var. Red Kidney. Nucleic acid levels were determined as were phosphate pool sizes in conjunction with (32)P labeling patterns. Each of these parameters indicated a mobilization into the tissues proximal to the zone of cellular separation at the expense of the distal tissues, suggesting that mobilization and the consequent development of cellular senescence provide a component in the process of bean leaf abscission.