The inter-relationship between putative cholinergic and noradrenergic innervation of the human adrenal cortex was investigated using a technique which combined acetylcholinesterase histochemistry, choline acetyltransferase radiochemistry and dopamine beta-hydroxylase immunohistochemistry. Cholinergic and noradrenergic nerve fibres had a near-identical distribution, with varicose noradrenergic fibres located immediately alongside non-varicose cholinergic nerve bundles in all cortical zones. Choline acetyltransferase activity was consistently detected in the adrenal cortex, confirming the presence of cholinergic neurons. It is postulated that noradrenergic innervation has a role in the modulation of cortical endocrine secretion, while cholinergic nerves are mainly concerned with the control of medullary secretion.