The relationship between both DNA and RNA metabolism and the nerve growth factor (betaNGF)-induced differentiation of PC12 cells was investigated. Cells remained in log phase growth for 4 days after exposure to betaNGF. DNA synthesis was similarly unaffected by betaNGF during this time. Thereafter, a gradual decrease in DNA synthesis was observed. In contrast, as many as 40% of the cells display neurites after 4 days exposure to betaNGF. The implication, that cells which have begun to differentiate morphologically may still synthesize DNA, was confirmed using autoradiography. The cellular RNA concentration was elevated significantly within 1 day of exposure to betaNGF and continued to increase for up to 6 days. Dose-response analysis revealed that this increase in cellular RNA, both rRNA and tRNA, closely correlates with the size and number of neurites per cell rather than with the cell's capacity to grow a neurite per se. A parallel rise in the cellular protein concentration was observed also. It was concluded, therefore, that (1) cessation of cell division is not a prerequisite for the initiation of the morphological differentiation of these cells and (2) the elevation of the cellular RNA content influences some quantitative aspects of neurite outgrowth.