Previous experiments have demonstrated that 4 S RNA is transported axonally during the reconnection period of optic nerve regeneration in goldfish. The present experiments were performed to determine whether 4 S RNA is transported axonally during later, maturational stages of nerve regeneration and to examine some of the characteristics of 4 S RNA in regenerating axons. [3H]Uridine was injected into both eyes of fish 18 days (near the time of reconnection) after bilateral optic nerve crush and the fish were sacrificed at various times up to 180 days after injection. [2H]RNA was isolated by phenol extraction and ethanol precipitation from 24 pooled tecta and fractionated by SDS- polyacrylamide tube gel electrophoresis. Data from these experiments showed that 70% of the [3H]RNA is present as 4 S RNA 12 days after injection, and 60 days after injection, this value is still approximately 50%. When nerves were cut 36 days after injection (54 days post-crush) and allowed to degenerate for 6 days before determining tectal [3H]RNA, the majority of the 4 S[3H]RNA was lost from the tectum. This indicates that up to 36 days after injection, 4 S [3H]RNA remains within regenerating axons and that it is unlikely that significant amounts of axonally transported 4 S RNA are transferred out of the axon to surrounding cells. In other experiments, the time of sacrifice after injection was held constant and the time of injection after nerve crush was varied. Analysis of tectal [3H]RNA showed that the major period of axonal transport of 4 S [3H]RNA was in early stages of regeneration at 24 and 36 days after nerve crush and that the amount of 4 S [3H]RNA which is transported axonally decreased at later time points. Calculations of the amount of axonal 4 S [3H]RNA versus what is synthesized in periaxonal cells gave results suggesting that 4 S RNA in regeneration axons turns over relatively slowly when compared with 4 S RNA in tectal cells.