Glass microelectrodes were used to record the activity of neurones in the left dorsal horn of the L6 segment of the spinal cord of normal cats and cats in which the left sciatic and saphenous nerves had been cut 1 or 9 months previously. In the normal animals the receptive fields of L6 dorsal horn neurons excited by tactile stimulation of the leg were somatotopically organized, with neurones in the medial and central dorsal horn having receptive fields on the distal parts of the leg, particularly the toes, and neurones in the lateral dorsal horn having receptive fields on the proximal parts of the leg, buttock and lower back. This somatotopy has been shown before. One month after nerve section no cells responded to tactile stimulation of the distal leg and cells in the medial and central parts of the dorsal horn now had receptive fields on the proximal leg, buttock and back. There did not appear to be any somatotopic organization of these new receptive fields. Lateral dorsal horn neurones had normal receptive fields. Nine months after nerve section neurones in the medial and central parts of the lumbar dorsal horn had receptive fields on the distal leg but they showed several abnormal features and there was no evidence of a return of the somatotopic organization seen in normal animals. Lateral dorsal horn cells still had normal receptive fields.