Four monkeys were trained to open a door with either the right or left hand in response to a tactile stimulus to either leg. After unilateral frontal arcuate ablation inducing unilateral neglect, the response time on this task increased most when the monkey responded with the hand contralateral to the lesion, but also increased when the monkey used the hand ipsilateral to the lesion. The side of stimulation had no effect on response time. Control (anterior superior temporal) lesions did not cause neglect and only affected response time slightly in one monkey (using the limb contralateral to the lesion). We conclude that response time is increased in animals with unilateral neglect and that the increase results from a defect in intention to act (motor neglect) rather than from sensory neglect. © 1987, American Medical Association. All rights reserved.