We investigated the response of chronic neck and shoulder pain to decompression of the carpal tunnel in 38 patients with whiplash injury. We also determined the plasma levels of substance P (SP) and calcitonin gene-related peptide (CGRP), which are inflammatory peptides that sensitise nociceptors. Compared with normal control subjects, the mean concentrations of SP (220 v 28 ng/l; p < 0.0001) and CGRP (400 v 85 ng/l; p < 0.0005) were high in patients with chronic shoulder and neck pain before surgery. After operation their levels fell to normal. There was resolution of neurological symptoms with improvement of pain in 90% of patients. Only two of the 30 with chronic neck and shoulder pain who had been treated conservatively showed improvement when followed up at two years. In spite of having neuropathic pain arising from the median nerve, all these patients had normal electromyographic and nerve-conduction studies. Chronic pain in whiplash injury may be caused by 'atypical' carpal tunnel syndrome and responds favourably to surgery which is indicated in patients with neck, shoulder and arm pain but not in those with mild symptoms in the hand. Previously, the presence of persistent neurological symptoms has been accepted as a sign of a poor outcome after a whiplash injury, but our study suggests that it may be possible to treat chronic pain by carpal tunnel decompression.