We have shown that overexpression of Bcl-x can rescue sympathetic neurones from nerve growth factor deprivation in vitro. We have also examined the distribution and expression of Bcl-x mRNA in the developing and adult nervous system using Northern blot and in situ hybridization. Bcl-x mRNA is widespread during development of the nervous system. In embryonic spinal cord, mRNA levels increase at the beginning of the naturally occurring cell death period, suggesting that Bcl-x may be involved in the selection of neurones during this period. In the brain, Bcl-x expression increases after birth to reach a high level in the adult brain. Neurones from the cortex, olfactory bulb, and Purkinje cells are among those expressing the highest levels of Bcl-x mRNA. The widespread expression of Bcl-x during development and in adult brain suggests of a role for Bcl-x beyond simply protecting neurones from developmental cell death.