Immunohistochemical detection of the neurone-specific ubiquitin hydrolase protein gene product 9.5 (PGP 9.5) has been applied to the normal adult human adrenal cortex to define overall patterns of innervation. Three distinct types of nerve morphology were noted in the cortex: large nerve trunks traversing the cortex to the medulla, a complex, branching network of slender nerve bundles and individual nerve fibres. These were more abundant in the head and body than in the alae and tail. Varicosities suggested local neurotransmitter release. Nerve fibres were also identified in the muscular wall of the central vein, which are apparently neither noradrenergic nor cholinergic. These data are in support of a direct role for nerves in the control of adrenocortical function and/or vascular responses in man.