The aims of this study were to investigate the anesthetic effects of medetomidine-midazolam-ketamine (MMK) combination and to compare antagonistic effects of atipamezole and yohimbine in dogs anesthetized with MMK. Eighteen adult male healthy beagles were used in this study. All dogs were anesthetized with intramuscular (IM) administration of medetomidine (0.04 mg/kg), midazolam (0.2 mg/kg) and ketamine (5 mg/kg) in one syringe. Intravenous (IV) administration of atipamezole (0.24 mg/kg, MMKA), yohimbine (0.2 mg/kg, MMKY) or saline solution (0.1 ml/kg, MMK) was administered 20 minutes after MMK combination anesthesia. Induction and recovery times, scores of sedation and analgesia, heart rate, blood pressure, rectal temperature, respiratory rate and blood gases were determined and recorded for each dog. Mean anesthesia times, sternal recumbency times, standing times and walking times in the MMKA and MMKY groups were significantly shorter than those in the MMK group. But there were not significantly different between MMKA and MMKY groups. In all groups, MMK administration produced a satisfactory sedation and analgesia for all dogs. However, after administration of atipamezole or yohimbine the scores for posture and response to noxious stimuli were significantly lower in the MMKA or MMKY group than those in the MMK group. MMK produced good sedation and anesthesia effects, and atipamezole or yohimbine can be used as a safe and effective agent for antagonizing the MMK anesthesia in dogs.