We have examined the distribution of probable cholinergic nerves in the human adrenal cortex using acetylcholinesterase (AChE) histochemistry. Adrenal tissue was obtained from three subjects during therapeutic radical nephrectomy for renal neoplastic disease. Light microscopy revealed a heterogeneous pattern of cortical innervation, with nerves most abundant in the head and body and largely absent from the tail. There was frequently a subcapsular plexus of interwoven AChE + ve nerve trunks in close relationship to densely stained (ganglion) cells. Nerves also traversed the zona fasciculata in radial trunks and a further plexus with ganglion cells was observed in the zona reticularis. Nerve trunks were seen to penetrate the medulla. Some nerve trunks appeared to terminate or branch or form individual nerve fibres (often with varicosities) which ramified through the cortical parenchyma. In the medulla, a generalised granular staining was superimposed on nerve trunks which were branched and interwoven to form a plexus around ganglion cells. The presence and distribution of AChE + ve nerve plexuses and varicose nerve fibres is suggestive of a functional intrinsic, probably cholinergic, innervation to the human adrenal cortex, perhaps derived from the splanchnic nerves.