Abstract The in situ isolated rodent larynx preparation can be utilized for the detection of peripheral opiate receptor antagonists. Measurements of peripheral opioid-induced laryngospasm and central opioid-induced respiratory depression can be made in each preparation. Fentanyl citrate was used to stimulate both peripheral and central opiate receptors and [ d-Ala 2-Met 5] enkephalinamide was used to stimulate only peripheral opiate receptors. Compounds that inhibit both laryngeal and respiratory effects of fentanyl, e.g., naloxone HCI, can be considered both central and peripheral opiate receptor antagonists. Compounds that inhibit only the peripheral laryngeal effects of fentanyl, e.g., naltrexone methylbromide, can be considered peripheral opiate receptor antagonists. The description of this preparation provides a simple and sensitive anesthetized animal model for the detection and characterization of compounds acting at peripheral and/or central opiate receptors.