Dorsal root ganglia from 8-day chick embryos can be stimulated to extend nerve processes in culture by inclusion of cytosine arabinoside (Ara-C) in the culture medium, in the absence of exogenous nerve growth factor (NGF). The degree of stimulation is dose dependent, and is not mimicked by either free cytosine or free arabinose. Since Ara-C is known to inhibit DNA synthesis, other inhibitors of DNA synthesis were tested. Hydroxyurea, fluorodeoxyuridine, and 3 mM thymidine all stimulated nerve outgrowth in the absence of exogenous NGF. In addition, bromodeoxyuridine also stimulated nerve outgrowth. In all cases, stimulation was observable after 24 h of culture, with maximal outgrowth achieved by 72 h of culture. The experimental response was never as large as the response to NGF, but was up to seven times greater than control outgrowth. In all cultures, nerve processes were characterized by growth cones at their distal tips, colchicine-sensitivity, and a high tubulin content visualized by immunofluorescence with anti-tubulin antibody.