Dorsal root ganglionic cells, from 8-day chick embryo, undergo anabolic declines when incubated in vitro without Nerve Growth Factor (NGF) or other supportive agents. To determine whether the decline could be opposed by delayed administration of the NGF, cells were incubated without the factor for varying times, then supplies with it and tested periodically with pulses of radiouridine or radioleucine. The decline in RNA labeling was actually reversed by a delayed addition of NGF, and the effect was fully elicited within less than 10 min from the treatment. With delays up to 6 hr, this rapid activation by NGF fully restored the incorporation rate exhibited by fresh cells or by cells continuously incubated with NGF. From the hour 8 on, the NGF-induced activation of RNA labeling fell progressively shorter of restoring maximal performance until, by 18 hr, it was no longer significant. The residual (irreversible) decline in RNA labeling, starting after 6 hr, developed with a time pattern coincidental with that of the irreversible decline in protein labeling also displayed by those untreated cells, and similar to the appearance of RNA degradation and the acceleration of protein degradation. All four such "degenerative" events were fully prevented by NGF when administered with delays shorter than 6 hr, and only interrupted (or delayed) by NGF delivered at later times. Additional experiments revealed that, over the first 6 hr, NGF also prevented or reversed a decline in TCA-soluble radioactivity of the cells, an effect which was not blocked by actinomycin D. This rapid increase of soluble radioactivity could be responsible for the rapid activation of RNA labeling and may also be involved in the prevention by NGF of the later developing degenerative events.