The unstabilizing action of very low concentrations of anticholinesterase agents on the cereal nerve-giant fiber synapses in the last abdominal ganglion of the roach, Periplaneta americana (L.) (Roeder, Kennedy and Samson, 1947; Roeder, 1948 and Roeder and Kennedy, 1955) as well as identification of acetylcholine in insect nervous tissue (Lewis, 1953; Augustinsson and Grahn, 1954;) suggest that acetylcholine is involved in synaptic transmission in insects. However, although low concentrations of acetylcholine have been shown to increase the rhythmic contractions of the roach heart (Krijgsman and Krijgsman, 1950) and intestine (Kooistra, 1950), even very high concentrations (1.0%) of acetylcholine had no consistent effects when applied directly to the last ganglion (Roeder, 1948). Tobias, Kollros and Savit (1946) found that between 7 and 10 gms. acetylcholine must be injected per kg. of roach to produce convulsions and death. Demonstration by Hoyle (1952, 1953) that the connective tissue sheath which envelops the insect nervous system restricts the diffusion of potassium ions lent support to a hypothesis that externally applied or injected acetylcholine may fail to reach the interior of the ganglion in effective quantities rapidly enough to stimulate. Recent studies (Twarog and Roeder, 1956) indicate that the sheath surrounding the abdominal cord of the roach is indeed a barrier to the diffusion of acetylcholine as well as sodium and potassium ions. In connection with these last studies, a method was developed for the simple and effective desheathing of ganglia and connectives of the roach abdominal cord.