Four combinations of drugs--ketamine-xylazine, ketamine-xylazine-acepromazine (KXA), ketamine-xylazine-buprenorphine, and ketamine-xylazine-carprofen--were compared for their ability to produce anesthesia in BALB/c mice. Induction time, anesthetic duration, blood pressure, pulse rate, and time to recovery were recorded. The anesthesia induced by each anesthetic combination was assessed by using reflex responses to standardized stimuli. The KXA combination produced stable physiologic parameters and was associated with the longest duration of anesthesia (40 +/- 8 min); immobility was produced in all other groups (38 +/- 5 min), but a surgical plane of anesthesia could not be confirmed. All anesthetic protocols produced significant hypotension. No deaths occurred. We recommend KXA as a safe and reliable anesthetic for mice requiring a surgical plane of anesthesia.