1. An enzyme similar to mammalian acetylcholinesterase is found in high activity in the nervous tissue of Palaemonetes varians, i.e. eyes plus stalks, brain, suboesophageal ganglion and ventral cord. Acetylcholinesterase is also found associated with the abdominal muscles. Multiple enzyme forms are found in extracts of nervous tissues and muscles by electrophoresis and isoelectric focusing. 2. Cholinesterase is present in high activity in the stomatogastric system of P. varians. Three electrophoretically separable forms are found, having isoelectric points at pH4.2, 4.5 and 5.4. 3. Approx. 50% of the total acetylcholinesterase activity, approx. 80% of the choline acetyltransferase activity and 100% of the acetylcholine equivalents are found associated with the nervous tissue. Among the tissues examined, eyes plus stalks were the richest source of both choline acetyltransferase and acetylcholine equivalents. Suboesophageal ganglion and brain also contained large amounts of these components. 4. The distribution of these components could support the function of acetylcholine as a central and/or sensory transmitter in P. varians.