The cholinergic innervation of the human axillary sweat glands of hyperhidrotic patients was demonstrated by using the specific Karnovsky-Roots thiocholine method. The cholinergic innervation pattern was compared with the immunohistochemically demonstrated vasoactive intestinal polypeptide (VIP)-like activity at light and electron microscopic levels. The innervation patterns were identical in the light microscopic serial sections. In the electron microscope sections, VIP-like immunoreactivity was localized to the nerve terminals containing large, dense-cored vesicles 100-140 nm in size. No synapses were found, however positively stained nerve terminals were located immediately outside the basement membrane but close to the glandular secretory and myoepithelial cells, blood vessels, and occasionally the mast cells. Our results suggest the coexistence of the two neurotransmitters, acetylcholine and VIP, in the same nerves innervating both eccrine and apocrine sweat glands in human axillae.