We examined 15 dermal neurofibromas from five adults with disseminated neurofibromatosis. All tumors contained axons that reacted for catecholamines and tyrosine hydroxylase on histochemical stains. Assay of tissue homogenates identified norepinephrine as the catecholamine. Assays for dopamine and choline acetyltransferase were negative. Some axonal components of dermal neurofibromas may originate in sympathetic adrenergic neurons. Most dermal neurofibromas do not contain neuronal cell bodies, and some of the axons may maintain functional connections with proximal sympathetic neuronal cell bodies. Sympathetic denervation may therefore affect the growth of these dermal neurofibromas.