['Single-fibre extracellular action potentials were recorded with 2 pairs of wire electrodes from lower human sacral nerve roots during surgery. The roots from which was recorded from were used for morphometry. Nerve fibre groups were identified by conduction velocity distribution histograms of single afferent and efferent fibres and partly by nerve fibre diameter distribution histograms. The values of group conduction velocity and group nerve fibre diameter measured in the paraplegics were very similar to those obtained from brain-dead humans and patients with no spinal cord injury. Thus the classification and identification of nerve fibre groups remained preserved following spinal cord injury. Upon retrograde bladder filling the urinary bladder stretch and tension receptor afferent activities were increased; on two occasions they even fired when the bladder was empty. Two reasons are brought forward for a too small storage volume of the urinary bladder in paraplegics: too high afferent activity of the bladder due to changed receptor field transduction mechanisms and too low compliance.'] Is the classification and identification of human somatic and parasympathetic nerve fibres including urinary bladder afferents and efferents preserved following spinal cord injury?