Nerve growth factor (NGF) can promote the out growth of neurites of the target ganglia. In order to further explore the relationship between this effect and the synthesis of RNA and DNA in the neurons, and autoradiography of 3H-uridine and 3H-thymidine was used. Superior cervial ganglia (SCG) from newborn rats were culivated by Maximow's double coverslip method. All cultures were divided to one group of cultures a crude preparation of NGF was added to the medium and another group without NGF served as control. Before tissue culture was stopped, the coverslip cultures were transferred to the labeling-medium and incubated, and then they were fixed, and cut into serial sections and subjected to autoradiographic processes. The results show that the percentage and the level of grains of neurons labeled by 3H-uridine in the NGF group are higher that that of control. Moreover, before the growth rate of neurites reaches a peak, the level of grains of neurons labeled by 3H-uridine in the NGF group is obviously increased. The evidence suggests that NGF can promote the synthesis of RNA in neurons of SCG, which has a direct bearing on the quick outgrowth of neurites. In the experiments with 3H-thymidine incorporation, that the NGF may promote the synthesis of DNA in some neurons of the third day SCG in vitro was also observed.