The main defective manifestations of extra-personal unilateral spatial neglect concern the side of space contralateral to the hemispheric lesion (contralesional). Since the disorder is more frequent and severe after damage to the right hemisphere, patients typically fail to explore the left side and ignore stimuli located in that sector of space. The patients' behaviour in the side of space ipsilateral to the side of the lesion (ipsilesional) is not intact, however. In cancellation tasks, it can be observed that patients with unilateral neglect, in addition to failing to respond to contralesional stimuli, may show perseverative behaviour, crossing out many times the same stimulus in the ipsilesional side of the sheet. We analyzed the occurrence of this phenomenon during the execution of a cancellation task in a large series of brain-damaged patients with left- and right-sided hemispheric lesions, with and without evidence of unilateral spatial neglect, and in a group of patients suffering from senile dementia of the Alzheimer-type. Perseverative responses were found to be much more frequent in patients with spatial neglect and when the frontal lobe or subcortical structures were damaged. The results are interpreted in the context of a multi-componential view of the neglect syndrome, with reference to a distinction originally put forward by Derek Denny-Brown (1958) between 'frontal or magnetic' and 'parietal or repellent' apraxia. In patients with spatial neglect, frontal damage releases drawing perseverative behaviour in the ipsilesional sector of space. Perseveration in exploratory tasks constitutes a main instance of the productive manifestations of spatial neglect.