The effects of intrathecal baclofen infusion were studied in 9 spinal cord injury patients whose spasticity had been refractory to oral medications. In a two stage, placebo controlled trial, baclofen was administered into the lumbar intrathecal space and subsequent clinical and neurophysiologic changes were assessed. In stage 1, 9 patients underwent a 5 day percutaneous infusion of baclofen and placebo via an external pump. Ashworth and reflex scores were assessed at time of enrollment, after infusion of that amount of baclofen which provided optimal spasticity control and after intrathecal infusion of placebo. The mean Ashworth grade decreased from 3.78 +/- 1.34 to 1.16 +/- 0.48 (p less than 0.001) while mean reflex score decreased from 3.57 +/- 1.05 to 0.64 +/- 0.87 (p less than 0.001). These values differed significantly from those associated with placebo therapy (Ashworth grade--2.54 +/- 1.04, p less than 0.001; reflex score--2.56 +/- 1.04, p less than 0.01). Objective improvements in functional abilities and independence were noted in 8 patients, while somatosensory and brainstem auditory evoked potentials were unchanged in all patients. Urodynamic evaluation revealed increased bladder capacity in 3 patients, while in 4 no change was observed. In Stage 2, permanent programmable infusion pumps were implanted in 7 patients who demonstrated a good response during Stage 1. In this group, mean Ashworth score decreased from 3.79 +/- 0.69 to 2 +/- 0.96 (p less than 0.001) and mean reflex score decreased from 3.85 +/- 0.62 to 2.18 +/- 0.43 (p less than 0.001). Baclofen dosage increased from 182 +/- 135 to 528 +/- 266 mcg/day over the 3-22 month follow-up period. Most of the dosage increase occurred within the initial 12 months following infusion pump implantation and tended to plateau thereafter. Minor complications such as catheter dislodgement/kinking and nausea occurred infrequently while no device related infections were observed. There was no clinical evidence of any significant baclofen neurotoxicity either in Stage 1 or 2. The only ambulatory patient developed marked lower extremity weakness during Stage 1 intrathecal baclofen infusion and was temporarily unable to walk. We conclude that continuous administration of intrathecal baclofen is an effective and safe modality for spasticity control in patients who are refractory to oral medications.