Patients with Parkinson's disease (PD) have dysfunction in frontal-basal ganglia networks. Many of these patients have difficulties with mental processing speed, response inhibition, and shifting between different conceptual sets, suggesting frontal-executive dysfunction. Since frontal lobe dysfunction is associated with disengagement deficits such as perseveration and echopraxia we wanted to learn if patients with PD demonstrated defective response inhibition. Using a brief clinical test called the crossed response inhibition (CRI) task we assessed patients with PD (n = 17), and a group of age matched controls (n = 30). In addition to the CRI, subjects were asked to perform two tests of frontal lobe function: verbal word fluency, anti-saccade test. In the CRI task, patients are instructed to lift the hand opposite to the one the examiner touches. An error is scored whenever the patient makes any movement of the touched (ipsilateral) extremity after stimulation (from shoulder to fingers). The task is performed with the patient's eyes closed. Whereas no differences were found between PD and control subjects on the verbal fluency or anti-saccade tasks, PD patients made significantly more errors on the CRI than did controls. Subsequent analyses found no difference in performance associated with the laterality (asymmetry) of PD symptoms or signs. In addition, there was no difference between PD patients' CRI performance when they were "on" their dopaminergic medications versus when they were "off" these medicines. Based on these findings, it appears that PD is associated with a disengagement-inhibition defect that is not induced by a dopaminergic deficit. In addition, the CRI task might be a brief sensitive bedside task for evaluating frontal dysfunction in PD.