Ion and oxygen uptake were studied on aging bean stem slices. Oxygen uptake was high immediately after slicing, decreased to a minimum at 100 minutes, and then increased again. Ion uptake per unit of O2 uptake data suggested that metabolic energy was utilized almost exclusively for sodium transport in fresh tissue but was diverted to potassium transport as the slices aged. Oxygen and ion uptake in fresh slices was less sensitive to 2,4-dinitrophenol as compared to the aged slices, indicating major metabolic and physiological changes occurred during aging. This was further substantiated by the tissue response to cyanide and antimycin A. Oxygen uptake was decreased by cyanide (22% by 1 mm) and antimycin A (14% by 1 microgram per milliliter) in fresh slices but not in aged slices. Potassium uptake that developed during aging was sensitive to cyanide and antimycin A. The results are pertinent to understanding the role of the stem in regulating ion transport in plants.