The electromyographic activity evoked by forced ankle rotation in spastic patients with cerebral palsy differs markedly from that found in normal subjects or in patients with adult-onset injuries to the central nervous system. Rapid dorsiflexion can produce a strong myotatic reflex electromyogram at 30 to 50 msec in the normal adult's stretched soleus muscle, while the antagonist tibialis anterior muscle quiet. The same is true of spastic patients whose injury has an adult onset. In patients with cerebral palsy this early response is found in both muscle groups. The pattern of "reciprocal excitation" is in marked contrast to the reciprocal inhibition normally seen. This reflex behavior suggests a fundamental developmental error in neuronal interconnections of the spinal cord in cerebral palsy.