Applications of auxin to the tips of intact aged pea Pisum sativaum L. var Alaska epicotyls resulted in an increase in the content of polyribosomes and poly(A) and in the capacity of isolated polysomes to support protein synthesis in vitro. Few changes were seen in the two-dimensional gel patterns of silver-stained proteins accumulated (or degrded) in vivo even after 15 hours of auxin treatment. In contrast, substantial changes were evident in the two-dimensional gel fluorographs of polypeptides generated in vitro by total RNA and by polysomal RNA from tissue treated with auxin for only 6 hours. Of the 200 spots resolved by fluorography, total RNA from auxin-treated tissue generated 33 spots with increased intensity and 10 with decreased intensity; polysomal RNA yielded 33 spots which increased and only three that decreased. In general, the polypeptides that increased in intensity were higher molecular weight and those that decreased were lower molecular weight. These changes occurred prior to growth and might be prerequisite for the auxininduced slow growth response seen in this aged tissue.Comparisons were made between the changes in RNA and protein metabolism occuring during aging and after wounding and auxin treatment of aged tissue. Aging causes a decline in poly(A), polysomes, and protein synthesizing capacity, whereas wounding and auxin treatment cause increases. Wounding appears to act primarily at the level of translation, whereas auxin has a greater effect on transcription. It is argued that the use of excised tissue to study auxin effects on RNA and protein metabolism should be avoided.A tremendous amount of evidence had accumulated until the late 1960s to support the contention that RNA and protein synthesis were required for auxin to induce growth in a wide variety of tissues (8). However, at about that time fast growth responses to auxin were discovered and it was argued that these responses to auxin were too fast to involve RNA synthesis (6). For the next 10 years, the fast growth theory, and its compatriot, the acid growth theory, held sway (14). A decade later, Vanderhoef (18 and references therein) postulated that auxin evokes two responses, one rapid but short-lived, for which RNA and protein synthesis may not be required, the other slower to develop but of greater duration for which RNA and protein synthesis are required.