It has now become possible to measure pain thresholds in man by the threshold or amplitude of the leg flexion nociceptive reflex (RIII reflex). These parameters accurately reflect the pain levels perceived by the patients. The aim of the present study was to assess pain thresholds in Parkinsonian patients, using the RIII reflex. Painful phenomena are often mentioned in Parkinson disease, but the perceived pain threshold level can be difficult to assess because of the depressive symptoms which are often associated with Parkinson disease. In 8 cases out of 10, the pain threshold was found to be higher in patients with Parkinson disease than in a control population of the same age: in 2 cases, naloxone injection led to recovery of the normal pain threshold level.