The hypothesis to be verified is that the cognitive defects in nondemented and nondepressed Parkinsonians are due solely to a bilateral nigrostriatal disorder that causes motor slowing. It was tested on 26 mildly disabled patients with idiopathic Parkinson disease optimally controlled with L-Dopa, nondemented and nondepressed and not receiving anticholinergic. The test used was a simplified version of the London Towers Test of problem-solving ability, designed to measure a facet of prefrontally-induced bradyphrenia, already calibrated on 131 healthy subjects. The results revealed no significant difference between the Parkinsonians and controls, thus providing no support for the hypothesis in question.