This double blind cross-over study, involving 9 chronic spinal cord injured (SCI) patients (6 paraplegic and 3 paretic), was a first attempt to investigate the effects of the noradrenergic agonist, clonidine, on the modulation of the locomotor pattern and spasticity in patients with spinal cord lesions. Electromyographic (EMG), footswitch and video recordings were made as the patients walked on a treadmill with the support of an overhead harness if needed. Overground locomotion was also assessed in the paretic patients. All 3 spastic paretic patients had kinematic deviations and abnormal EMG recruitment profiles during the premedication or placebo sessions. With clonidine therapy one patient demonstrated a marked improvement in locomotor function. This patient progressed from non-ambulation to limited independent ambulation as the extent of coactivation in antagonist muscles decreased. The other 2 paretics who presented limited spasticity showed minimal changes while on clonidine. In the paraplegic patients, clonidine did not elicit locomotor activity, although there were marked reductions in stretch reactions and clonus during assisted locomotion. They remained incapable of locomotion, either during the control period or during the clonidine therapy. These results indicate that clonidine may be a potentially useful medication for both locomotion and certain manifestations of spasticity in SCI patients but further investigation is warranted.