In a double-blind study, we evaluated the intramuscular administration of modified neurotoxin in 48 patients who were treated for 6 months. There was no evidence to support claims that patients receive any benefit from the neurotoxin. A significant number of patients had minor functional improvement, often of a transient nature, but these manifestations were more common in the placebo-treated patients than in those receiving neurotoxin. These variations in the course of motor neuron disease have not been stressed in the previous literature.