SEVERAL convulsant drugs have been shown to act by impairing specific inhibitory processes in the brain, and there is a clear-cut contrast between crustacean and mammal in this respect. In the crayfish, picrotoxin produces convulsions and it blocks several inhibitory mechanisms as well as the inhibitory action which Florey's Factor I exerts on these synapses1–3. Strychnine does not cause convulsions in the crayfish nor does it interfere with these inhibitory processes1,2. In the cat both drugs act as convulsants; but only strychnine antagonizes the inhibitory post-synaptic potentials of spinal motoneurones4,5 and the centrifugal inhibition mediated by the Rasmussen's olivocochlear fibres, both crossed6 and uncrossed7. The mode of action of picrotoxin in the mammalian brain is less clear and it may involve an activation of excitatory synapses8. The pharmacological approach just sketched clearly provides useful tools for the investigation of neural inhibition and of convulsive states, and it seemed worth extending it to the bird, using as a physiological test the inhibition produced by the efferent cochlear bundle9, which can be successfully stimulated as follows10.