Fasciculations secondary to succinylcholine injection were prevented in surgical patients by pro treatment with adequate doses of procaine and lidocaine. Lidocaine was more effective in equal dosage. The protective effect did not appear to depend on circulatory factors or inhibition of the plasma cholinesterase system. The site of action appears to be at the myoneural junction, suggesting an effect on the acetylcholine system and pre-synaptic membrane.