Patients suffering from sciatica may develop altered patterns of corticospinal drive to muscles of the leg. Electromyographic recordings were made bilaterally from tibialis anterior and lateral gastrocnemius muscles during transcranial magnetic stimulation of the motor cortex from nine patients with unilateral sciatica and seven healthy controls. The mean thresholds for eliciting motor evoked potentials (MEPs) and the silent period were higher in the patients than in the control subjects. In addition, there was a positive correlation between the patients' self rated score of disability (the Oswestry Disability Index) and their threshold for MEPs and the silent period. This study suggests that the chronic pain experienced by the patients leads to a reduction in corticospinal drive to the legs. These changes might help to relax muscles close to the perceived site of pain and so alleviate symptoms. Investigation of these patients following remedial treatment will allow us to establish if the changes are transient in nature.