The red nucleus is a prominent brainstem nucleus in mammals which is thought to be involved in production of skilled limb movements. The presence of the red nucleus and associated rubrospinal tract in animals that do not produce skilled limb movements, however, suggests that these structures might also be involved in control of more general limb actions, such as those occurring during locomotion. The present study investigates this question by measuring the three-dimensional ground reaction forces produced by locomoting rats with unilateral excitotoxic lesions of the red nucleus. Twenty-four to 48 h after the lesion, rats moved with an asymmetric gait during which abnormal braking and propulsive forces were produced during the dual contact time of the forelimb contralateral to the lesion and the ipsilateral hindlimb. Rats did not recover normal symmetrical locomotion within the 55-day duration of the study. The persistent asymmetry produced by red nucleus ablation provides the first unequivocal demonstration that the red nucleus plays a role in ongoing overground locomotion in the rat. Species differences in phylogeny and connectivity of the red nucleus are discussed, as well as the possibility that there is a general compensatory response to unilateral CNS injury in the rat.