Difficulties in shifting of cognitive sets and perseverative behaviour have been shown to be part of the neuropsychology of Parkinson's disease, possibly due to frontal dysfunction. We have tested perseverative motor behaviour by assessing ability to generate random movement sequences in 15 patients with Parkinson's disease using the Breidt Perseveration Test Device (PTD). In this experiment subjects are instructed to press one of nine buttons arranged randomly on a metal board without use of systematic or repetitive strategies. The speed of this task that comprises 150 consecutive presses is determined by an acoustic go-signal appearing at 1 Hz frequency. Results were compared with 14 age-matched controls. Patients performance was impaired with intrusion of unwanted systematic strategies suggesting a decreased ability of Parkinson patients to generate random movement sequences.