During hyperalgesia there is an enhancement of wind-up and the appearance of a novel wind-up of the A-fibre-mediated responses. We have examined if these phenomena are influenced by supraspinal mechanisms by analysing single motor unit activity in control and arthritic rats, either intact or acutely spinalised. Enhancement of the C-fibre wind-up and the novel A-fibre wind-up were only observed in the intact arthritic animals. We conclude that C-fibre wind-up is a spinal phenomenon, whereas the enhancement of the C-fibre wind-up and the novel A-fibre wind-up during arthritis depend also on supraspinal influences.