The observation in this series is simulating the finding that denervation causes a pronounced loss in the specific acetylcholinesterase activity. This lower acetylcholinesterase activity may have a correlation with the denervation supersensitivity phenomenon found in the isolated cortical slab and its homotopic area and the smaller decrease of acetylcholinesterase activity in the contralateral area may be indicative of presence of modulating nervous connections which the isolated slab is devoid of. Diminished cholinesterase activity in isolated and contralateral cortical slab in metrazol treated cases might suggest that excessively liberated acetylcholine is destroyed easily and there is a condition of nonavailability of the acetylcholine substrate for the activity of acetylcholinesterase. Caffeine treatment may cause higher synthesis with slower liberation of acetylcholine demanding increased activity of acetylcholinesterase.