Use of intramuscular botulinum-A toxin (Botox) to produce neuromuscular blockade has been effective in treating certain ocular and facial muscular imbalances as well as spasmodic torticollis. In this preliminary open study, the effectiveness of intramuscularly injected Botox on the muscular imbalances of cerebral palsy was assessed in 27 pediatric patients. Each patient had "dynamic deformities" unresponsive to other treatment, and operation was the only other realistic alternative. The dose of Botox was calculated on a unit/body weight basis. In ambulatory patients, clinical changes in gait were assessed by a physician's rating scale. Reduction in spasticity became apparent in 12-72 h after injection; the effect of Botox after target threshold was reached lasted 3-6 months. No major side effects occurred. Botox may prove a useful adjuvant in conservative management of the spasticity of cerebral palsy. Successful management with these injections may allow delay of surgical intervention until the child is older and at less risk of possible complications, including the need for repeated surgical procedures.