Neuroendocrine chromaffin cells of the adrenal gland express certain molecular markers either transiently during development or permanently. In the present study, the expression of neuromodulin (GAP-43), a neuronal protein often associated with neurite outgrowth, was examined in adult adrenals. Neuromodulin was detected by Western blot analysis in extracts of both rat adrenals and cultured bovine chromaffin cells, and was localized in situ in a subpopulation of chromaffin cells, as well as in nerve fibres and Schwann cells. The use of anti-tyrosine hydroxylase or anti-phenylethanolamine N-methyltransferase antibodies in combination with anti-neuromodulin antibodies in double immunofluorescent labelling of cryostat sections of rat glands demonstrated that neuromodulin is expressed by noradrenergic, and not by adrenergic chromaffin cells. The results provide further evidence that neuromodulin is not limited to neurons; it is also expressed in a subpopulation of neuroendocrine chromaffin cells. Neuromodulin may play a role in the development of the adrenal medulla or in the specific regulation of noradrenalin secretion from chromaffin cells.