1. Crystalline d-tubocurarine, dihydro-beta-erythroidine, quinine ethochloride, nicotine and thiamine inhibited and suppressed the electrical activity of the frog brain.
2. Prostigmine, which itself depresses brain potentials, failed to influence the effect of these substances on the brain potentials, although it counteracted their effects on the neuromuscular junction.
3. Prostigmine partially inhibited the electrical activity of the frog brain; a subsequent injection of acetylcholine suppressed the electrical activity completely.
4. Monoiodoacetic acid and sodium cyanide abolished the brain potentials of pithed frogs.
5. The findings are interpreted as an inhibition of central synaptic transmission by curare and substances with a curare-like action.