To investigate the relationship between the site of brain damage and characteristics of the pathological grasping phenomena, we examined different varieties of the reaction in a consecutive series of 28 patients with unilateral hemispheric damage due to stroke. Patients with a lesion relatively confined to the supplementary motor area (n = 4) constantly exhibited a grasp reflex, mainly in the hand contralateral to the lesion, but they never showed a groping reaction. By contrast, patients with damage primarily involving the anterior cingulate gyrus (n = 3) developed the groping reaction in the hand contralateral to the lesion, but they had only a very mild grasp reflex in that hand. Patients with damage involving both the supplementary motor area and the anterior cingulate gyrus (n = 12) showed the grasp reflex and groping reaction mainly in the hand contralateral to the lesion. Patients with damage to the medial parietal lobe (n = 2), those with damage to the lateral convexity of the hemisphere (n = 6), and a patient with damage confined to the corpus callosum did not exhibit such grasping phenomena. From these observations, we conclude that the grasp reflex is closely related to a lesion of the supplementary motor area, whereas the groping reaction is bound to a lesion of the anterior cingulate gyrus.