Ectopically generated and antidromically conducted nerve impulses were recorded in 5 patients with tungsten microelectrodes inserted into skin nerve fascicles. All patients had mainly positive sensory symptoms and reported paresthesiae which could be provoked by different maneuvers which suggested increased mechanosensitivity of the primary sensory neurons at different anatomic levels. Ectopic multiunit nerve activity correlating in intensity and time course to the positive sensory symptoms was recorded: when Tinel's sign was elicited in a patient with entrapment of the ulnar nerve at the elbow, when paresthesiae were provoked by elevation of the arm in a patient with symptoms consistent with a thoracic outlet syndrome, when paresthesiae were evoked by straining during chin-chest maneuver in a patient with an S1 syndrome due to a herniated lumbar disc, when a painful Lasegue's sign occurred during the straight-leg raising test in a patient with an S1 syndrome due to root fibrosis, and when Lhermitte's sign was elicited by neck flexion in a patient with multiple sclerosis. The sites for the ectopic impulse generation in these cases are suggested to be peripheral nerve, brachial plexus, dorsal root or dorsal root ganglion and dorsal columns. The paresthesiae were non-painful except in the patient with Lasegue's sign and the ectopic impulses were probably recorded from large myelinated afferent fibers.