This study was undertaken to evaluate the sedative effect of medetomidine, an α₂-adrenoceptor agonist, and the counteractive effect of atipamezole, an antagonist to medetomidine, in house musk shrews (Suncus murinus). Two hundred, 300, 400, or 600 μg/kg of medetomidine was intraperitoneal injected into 89 house musk shrews. A sedative effect was produced in one to two minutes after injection. The dose-dependent prolongation of the sedative duration and the dose-dependent appearance of a hypothermic effect were demonstrated. With 200 μg/kg of medetomidine, the sedative effect obtained was not adequate in some of the animals. With 300 μg/kg and above, a stable sedative state was induced in all the animals. The duration of sedation in the house musk shrews was much longer (p<0.01) in males than in females. This suggested the higher susceptibility of male house musk shrews to this drug. The sedative effect and hypothermia obtained with 400 μg/kg of medetomidine were completely counteracted by more than 2.0 mg/kg of atipamezole. With 0.5 and 1.0 mg/kg of atipamezole, only a partial antagonistic action was produced. Transient vomiting appeared in 4.5% of the house musk shrews at approximately one minute after injection of medetomidine. This side-effect had occurred before the sedative effect was obtained, and was not serious enough to be a problem. None of the 89 house musk shrews died in this experiment. The above results show that the combination of medetomidine and atipamezole is a highly effective and safe anesthetic treatment which permits easy handling of house musk shrews.