Comparative study of the anaesthetic effects of ketamine-medetomidine and tiletamine-zolazepam-medetomidine in the White-tailed Porcupine (Hystrix leucura) Introduction Anaesthesia of porcupines in zoos is often necessary for diagnostic and therapeutic procedures. Anaesthetic protocols for the chemical immobilization of porcupines vary. In the past, combinations of ketamine-xylazine and tiletamine-zolazepam have been described. In this study, medetomidine-ketamine was compared to medetomidine combined with tiletamine-zolazepam. Material and methods Twenty anaesthetic procedures of White-tailed Porcupines (Hystrix leucura) were evaluated. Animals were divided into two groups (A, B) of ten animals. Group A received 4.21 +/- 0.66 mg/kg ketamine and 84.22 +/- 13.13 mu g/kg medetomidine. Group B received 3.7 +/- 0.4 mg/kg tiletamine-zolazepam and 37.03 +/- 3.7 mu g/kg medetomidine. Anaesthesia was antagonized with 0.42 +/- 0.07 mg/kg atipamezole in group A and 0.21 +/- 0.02 mg/kg atipamezole and 0.01 +/- 0.001 mg/kg sarmazenile in group B (n=6). Four animals in group B received only atipamezole. During each 30-minute procedure respiratory rate, heart rate, SpO(2), mucous membrane colour, capillary refill time, eyelid and corneal reflex, muscle relaxation, analgesia and core body temperature were evaluated every five minutes. Additionally, first reaction time, lateral recumbency, standing time and recovery time were recorded for each porcupine. Results and Conclusion The main difference between group A and group B was observed during the recovery phase. The animals in group A had a smooth and uneventful recovery of 18:18 +/- 14:07 minutes and could quickly be returned to the enclosure. The four animals of group B that were antagonized with atipamezole alone showed first signs of recovery after 68:30 +/- 14:51 minutes (head-lift, standing up) but presented signs of re-narcotization for several hours after antagonizing. The remaining six animals in group B were thus administered sarmazenile in addition. Compared to group A, these animals still had a significantly prolonged recovery time of 85:40 +/- 54:14 minutes. During recovery, animals of group B were anxious, disoriented, ataxic and showed a lower fear response to the presence of humans. The animals had to be kept separately until they had recovered completely to avoid being attacked by other porcupines in the collection. The results of the study show that the combination of ketamine-medetomidine is superior for the anaesthesia of White-tailed Porcupines in a captive setting.