Parkinson's disease (PD) is frequently associated with freezing of gait. Patients with advanced PD learn to use tricks to relieve freezing of gait. Recently one of our patients informed us that he could overcome freezing of gait by crawling. Since crawling is a sort of quadruped gait that humans develop transiently, we wondered whether quadruped gait is preserved in PD. We recruited 16 patients with PD who had frequent and disabling freezing of gait. Under experimental conditions, after 12 hours without medication, seven patients developed biped freezing of gait. Of these seven patients, only two patients (the patients with the most severe freezing) also developed quadruped freezing of gait. This experiment suggests that bipedal gait is affected early in PD, while quadruped gait is preserved until late in this disease.