By means of intraneural micro recording (INMR) and intraneural microstimulation (INMS), properties of receptive units innervated by A delta and C fibers of the superficial branch of the radial nerve were measured on humans. Thresholds of 24 A delta units to mechanical stimulation varied significantly; their receptive fields ranged from a single point to 75.4 mm2, with one to four receptive sensitive zones. A delta units by INMS evoked tingling with projected fields varying between 1.2 and 97 mm2. Receptive fields and projected fields of these units overlapped each other and showed a proximodistal size gradient (P < 0.05). The results suggest that A delta units have accurate localizing capacity. Eleven nociceptive units had higher threshold to mechanical stimulation. INMS of C nociceptive units evoked burning pain. Both the receptive fields and projected fields of most of these units showed overlapping indicating that C nociceptive units, to some extent, can localize noxious stimulation.