This report demonstrates the use of the nerve bundle from the crayfish walking leg for the detection and assay of local anesthetics (LAs). Detection is achieved by monitoring the disappearance of the compound action potential (CAP) upon application of the local anesthetics to the nerves, pinned in a specially designed flow cell. CAP firing is induced with an electrical current pulse applied to the nerve bundle. Dose-response curves for the LAs tetracaine, lidocaine and procaine are constructed and factors which affect the detection are discussed. The application of this procedure to the screening for neurotoxicity and neuromodulatory activity of new drugs and natural product extracts is proposed.