[125I]Bolton-Hunter substance P [( 125I]BH-SP) binding sites in rat and human skin were investigated, using quantitative receptor autoradiographic and emulsion autoradiographic methods. [125I]BH-SP binding sites were discretely localized in skin areas anatomically corresponding to dermal papillae, sweat glands, and hair follicles. The highest density of the binding sites was in the dermal papilla of the finger, followed by the sweat gland. [125I]BH-SP binding to the dermal papillae of the human finger pad skin and rat paw pad skin was displaced by unlabeled SP, with a high affinity, and Kd values were calculated to be 744 pM and 297 pM, respectively. The existence of [125I]BH-SP binding sites supports the idea of the neurotransmitter role of substance P in skin dermal papilla.