Freezing, a symptom characterized by difficulty in the initiation and smooth pursuit of repetitive movements, is a unique and well known clinical feature of Parkinson's disease (PD). It usually occurs in patients with long duration and advanced stage of the disease and is a major cause of disability often resulting in falling. In PD patients freezing manifests most commonly as a sudden attack of immobility usually experienced during walking, attempts to turn while walking, or while approaching a destination. Less commonly it is expressed as arrest of speech or handwriting. The pathophysiology of Parkinsonian freezing, which is considered a distinct clinical feature independent of akinesia, is poorly understood and is believed to involve abnormalities in dopamine and norepinephrine neurotransmission in critical motor control areas including the frontal lobe, basal ganglia, locus coeruleus and spinal cord. In general, freezing is resistant to pharmacological therapy although in some patients reduction or increase in levodopa dose may improve this symptom. Three medicated PD patients exhibiting disabling episodes of freezing of gait are presented in whom brief, extracerebral applications of pulsed electromagnetic fields (EMFs) in the picotesla range improved freezing. Two patients had freezing both during "on" and "off" periods while the third patient experienced random episodes of freezing throughout the course of the day. The effect of each EMFs treatment lasted several days after which time freezing gradually reappeared, initially in association with "off" periods. These findings suggest that the neurochemical mechanisms underlying the development of freezing are sensitive to the effects of EMFs, which are believed to improve freezing primarily through the facilitation of serotonin (5-HT) neurotransmission at both junctional (synaptic) and nonjunctional neuronal target sites.