1. The central action of venom preparations from the digger wasp Philanthus triangulum on the cercal nerve-giant fibre preparation of the sixth abdominal ganglion of the cockroach Periplaneta americana, has been studied using the mannitol-gap technique. 2. At concentrations which are probably lower than the concentrations obtained after a sting of the wasp into the ganglion mass of the honeybee worker, certain venom preparations caused depolarization of the giant neurons, block of synaptic transmission and a concurrent depolarization of fibres in nerve XI. 3. The venom preparation possesses practically no anticholinesterase activity. 4. The centrally active components have not yet been purified, but have been separated from the components affecting neuromuscular transmission. 5. The active components probably have a molecular weight of less than 700. © 1982.