In situ hybridization combined with intraperitoneal injection of the tracer Fluoro-Gold was used to study the distribution of GAP-43 mRNA in autonomic cell groups of the rat spinal cord. In the thoracic cord, numerous cells expressing GAP-43 mRNA were present in the central autonomic nucleus (lamina X) and in the intermediolateral cell column (IML). In the IML, all Fluoro-Gold-labelled preganglionic neurones were heavily labelled for GAP-43 mRNA. In contrast, Fluoro-Gold-labelled motoneurones were unlabelled or only lightly labelled. Our results indicate that preganglionic sympathetic neurones express GAP-43, a conclusion that is consistent with studies showing that GAP-43 immunoreactive terminals are present in autonomic ganglia. GAP-43 in these neurones may play a role in their continuing anatomical remodelling.