We studied the effects of botulinum toxin A in 12 patients with spasticity and in eight patients with rigidity. The study design was a double-blind, placebo-controlled crossover trial with botulinum toxin A versus saline. Using the Ashworth Scale for spasticity and the Unified Parkinson's Disease Rating Scale for rigidity, we gave the patients a tone grade before and 2 weeks after treatment. Improvement in tone by two grades or more was considered clinically significant. In the spasticity group, botulinum toxin A reduced the tone of all patients significantly, improved functionality and nursing care in eight of 12 patients, and alleviated painful spasms in five of five patients. In the rigidity group, muscle tone was decreased in seven of eight patients, functionality improved in four of seven, and joint and muscle pain decreased in four of five. We conclude that botulinum toxin A is effective against the disabling effects of spasticity and rigidity. The treatment was well tolerated.