The process of the retrograde transport of nerve growth factor (NGF) has been recharacterized using a high specific activity preparation of[125I]NGF. Most of the general conclusions reached in the previous studies of Hendry, Thoenen and co-workers have been confirmed. However, significant quantitative differences were noted. Intraocular (anterior eye chamber) administration of[125I]NGF (less than 10 ng) resulted in accumulation in the superior cervical ganglia beginning at about 4 h. The ratio of radioactivity in the ipsilateral contralateral ganglia was 15--30:1. Maximal accumulation was seen at about 12h in the hamster and 16 h in rats. This pattern was quite different from that seen in other tissues. The uptake system from the eye of the rat was saturable (half-maximal at 15 ng) with maximal accumulation of 35--40 pg/ganglion. Systemic administration of[125I]NGF (200 ng) to adult rats resulted in no accumulation in SGG or celiac ganglion prior to 3 h, with subsequent rapid accumulation by 6 h and a rapid fall in radioactivity after 12 h. A similar time course was seen in 5-day-old rats, although the time curve was shifted slightly toward shorter time. The radioactivity in ganglia co-migrated with native NGF by SDS gell electrophoresis. Cytochrome c of comparable specific activity was not transported, and NGF did not stimulate the uptake and transport of cytochrome c. The retrograde transport of[125I]NGF was inhibited by the co-administration of biologically active, but not inactive, oxidized derivatives of NGF. By any route of administration, a significant percentage of the transported[125I]NGF was found in a purified nuclear fraction of the ganglia. Coupled with previous observations of specific nuclear NGF receptors in embryonic chick and sympathetic ganglia, this suggests that, after internalization and retrograde transport, NGF may directly act on the nucleus to produce at least some of its effects on the responsive cell.