Various trophic factors present in muscle extract can promote the survival of cultured motor neurones. However, little is known about the signal transduction pathways used in these cells. The proto-oncogene product p21ras has been shown to play an important role in proliferative and differentiative signalling pathways. We report here that cytoplasmic introduction of its oncogenic form, p21ras(G12V), fully supports the in vitro survival of chick embryonic motor neurones. The proto-oncogenic form of p21ras also showed a dose-dependent survival effect, while a C-terminally truncated counterpart of p21ras(G12V) was ineffective. These results suggest an involvement of p21ras in signal transduction pathways leading to motor neurone survival and may be of relevance for the development of therapeutic strategies for motor neurone disease.