The sequences and duration of support phases in the four-legged step cycles performed during unrestrained walking with moderate speed (0.4-1.0 m/s) were analyzed in two groups of cats: intact ones and animals with lesions of the ventral quadrants of the spinal cord at the low thoracic level. Spinal lesions resulted in a much greater variability of support patterns and an increase in the relative durations of the support on two ipsilateral limbs, accompanied by a reduction of support on two diagonal limbs. It is suggested that these changes reflected an impairment of fore-hindlimb coordination, due to an increased phase shift between the onsets of stance phases in the forelimb and in the contralateral hindlimb and may account, at least partly, for the unsteady and ataxic gait described in cats with ventral funicular lesions.