The clinical motor symptoms of basal ganglia disease are explored in relation to possible functions of this region of the human brain. It is concluded that Parkinsonian akinesia, and the dyskinesias of chorea, hemiballism and torsion dystonia are likely to represent the critical abnormalities of motor action in human basal ganglia lesions. These motor disorders involve most muscles, all classes of movement, and the individual sequential components of movement, but spare the overall motor plan. It is suggested that Parkinsonian akinesia is due to putaminal dysfunction disrupting the normal automatic execution of learned motor plans. The dyskinesias of chorea, hemiballism and torsion dystonia are conceived as being due to dysfunction of other strio-pallidal regions superimposed upon the normal function of the motor strio-pallidal system.