Two studies were conducted to investigate muscle recruitment of children with spastic cerebral palsy in response to unexpected perturbation of balance in stance. The aim of the studies was to investigate neural and non-neural mechanical contributions to muscle responses differences these children display when maintaining balance. In the first study, muscle responses of children with spastic diplegia were compared to typically developing children with similar levels of walking experience. Each child stood on a moveable platform that was displaced backward. Electromyographic recordings of posterior agonist and anterior antagonist muscles of the legs and trunk were analyzed and compared to those of normal children who had obtained a similar developmental levels of mobility. Children with spastic cerebral palsy were found to have an increase in antagonist recruitment and decreased trunk activation when compared to typically developing children at the same level of walking experience. Developmental trends were noted to be similar in all children with or without pathology. As children gained independent walking skills, they demonstrated shorter onset latencies in leg and thigh muscles. In the second study, older children with no pathology were perturbed in crouch stance, simulating the posture of their matched children with cerebral palsy. Changes in their muscle responses were observed to more clearly approximate the muscle onset latency organization of children with spastic diplegia. Results of these studies suggest that muscle recruitment differences for balance control in children with spasticity are due to CNS deficits as well as mechanical changes in posture. Copyright 1998 Elsevier Science B.V.