After nerve transection, the distal stump undergoes Wallerian degeneration (WD). Little information is available concerning sequential changes in nerve conduction measurements during WD in humans. Five patients with nerve injuries were studied temporally. Motor-evoked amplitudes were reduced by 50% at 3 to 5 days after injury; the response was absent by day 9. Sensory-evoked amplitudes were reduced by 50% at 7 days after injury; the response was absent by day 11. Sensory and motor nerves with shorter distal stumps showed earlier loss of amplitude than did those with longer distal stumps. Denervation potentials were seen 10 to 14 days after injury. Our results suggest that WD occurs earlier if the distal stump is shorter, and that motor-evoked responses are affected earlier than sensory-evoked responses. The time-lag between the loss of the motor-evoked response and the appearance of denervation potentials, the latter coinciding with reduction of sensory evoked responses, suggests that failure of neuromuscular transmission precedes axonal loss during WD.