Seven patients with spasticity of spinal cord origin have been maintained for up to 2 years with continuous spinal intrathecal infusion of baclofen. Prior to treatment, all of the patients had severe rigidity in their lower limbs and most had frequent and extensive spontaneous spasms, all of which greatly interfered with their activities of daily living. Oral antispasmodic medications were ineffective or caused central side effects. The patients underwent implantation of a programmable drug pump connected to a lumbar subarachnoid catheter. Within days of beginning continuous intrathecal baclofen infusion, the muscle tone was reduced to normal levels and spasms were eliminated. Over the ensuing months, muscle tone remained normal, but short-duration spasms could be induced by some activities. The greatest benefits to the patients were improvement in activities of daily living and better sleep due to reduced spasms. The baclofen doses were increased over the first few months but then were stabilized or only increased slightly, with the maximum dose being 650 micrograms/day. The most serious complications were two drug overdoses which took several days to clear up and were due to malfunctions of an earlier pump model. Baclofen clearance from the cerebrospinal fluid occurs with a half-life of 5 hours. The most serious concern in maintaining patients indefinitely on intrathecal baclofen is whether drug tolerance will eventually occur.