EMG activity of long foot flexor and extensor muscles was studied during gait in 34 ambulatory hemiparetic patients, correlating the EMG to phases of the gait cycle as monitored by switches placed on the plantar surface of the foot. EMG patterns during stance and swing phases were categorized into six groups, ranging from normal alternation of muscle contraction, to tonic activity of the extensors, with no alternation. The deterioration in activity appears to be related to the (unbalanced) release of extensor and flexor mechanisms which arises in varying degrees and combinations after capsular lesions. The extensor thrust postural reaction appears to be essential for gait in pathological conditions which result in upper motor neuron weakness.