We propose a double-masked placebo-controlled clinical trial combining treatment using the oral anti-spasticity medication baclofen with a 6-week program of strength training. We will enroll 20 ambulatory children with spastic diplegic cerebral palsy. Prior to and following the intervention, we will obtain quantitative measures of spasticity, strength, and gait. We predict that the children taking baclofen will have a greater increase in strength than the children taking placebo. We predict that the increase in strength will be reflected in improved performance on gait analysis, and it will correlate with a reduction in quantitative measures of spasticity and spinal reflex excitability.