BACKGROUND: American alligators ( OBJECTIVE: The objective of this study was to determine the analgesic efficacy of hydromorphone in alligators. METHODS: Female American alligators ( RESULTS: Administration of hydromorphone contributed to a range from 62 to 92% reduced avoidance reactions to mechanical noxious stimuli for two anatomic sites (i.e., naris and lateral mandible, respectively). CONCLUSION: Alligators did not appear to experience clinically relevant respiratory depression, hypothermia, or other adverse reactions. Therefore, hydromorphone shows promise as an analgesic option to be administered under painful conditions in American alligators.