Neuritogenesis, which occurs to a slight extent in chick embryo ganglia maintained under standard conditions and which is maximally stimulated by nerve growth factor, also was enhanced by presence in the medium of buffers (triethanolamine, Tris, and Hepes) and cytosine arabinoside and by the passage of direct electric current. The major effect of the buffers probably was to remove protons from cell membranes, that of the current to produce accelerated movement of ions through membranes of the ganglionic cells, and that of cytosine arabinoside to decrease the numbers of nonneural cells by inhibiting DNA synthesis. The buffers were neuritogenically ineffective on nerve growth factor-sensitive PC12 pheochromocytoma cells in culture. Media from ganglia in which triethanolamine or passage of electric current had elicited outgrowth of neurites produced no observable effect on PC12 cells under our experimental conditions. Current data fit the hypothesis that, whereas nerve growth factor exerts direct neuritogenic effects on neurons, the other treatments affect neural-nonneural interactions, possibly by way of gap junctions or changes in direct physical contact, so as to disinhibit inherent neural neuritogenic potential and/or to stimulate it.