During a 12-hr incubation low concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) enhance the metabolic breakdown of ribonucleic acid (RNA) whereas high concentrations of the auxin almost completely inhibit RNA breakdown after 4 hr of treatment. The data, from experiments where the incorporation of adenosine-8-C14 into RNA was followed, clearly show that the role of auxin in this system is not to appreciably alter net synthesis of RNA, but rather to alter some process(s) related to the degradative metabolism of RNA.