Movement and distribution of [14C]sucrose was studied in snapdragon flowers cultured on sucrose solutions in relation to the timing and extent of the characteristic reduction of nectar yield by 1AA, the question of whether IAA acts in the nectary cells or by reducing sugar movement to the nectary, and competition for sugar between nectaries and other tissues.There was a 50% reduction in accumulated nectar yield in flowers treated with IAA within 18 h; thereafter, the capacity to secrete nectar was virtually abolished. Within 6 h, IAA caused a significant increase in the incorporation of 14C into protein. Most of the 14C activity lost to nectar in flowers treated with IAA was recovered in the ethanol-soluble materials and protein of the flowers. Radioactivity continued to accumulate in the secretory tissue after secretion had stopped. The percentage reduction in nectar by IAA was not diminished under conditions of minimal growth and sugar transport distance. It was concluded that IAA acts on the secretory process in the nectary cells rather than on movement of sugar to the nectary.The influence of differences in sugar supply appeared mainly in the distribution of 14C activity between peduncles and nectar: as sugar supply was increased, a smaller percentage remained in the peduncles and a larger percentage was secreted. The secretory process competed strongly with floral tissues for sugar even when the latter were undersupplied.