This study was carried out to evaluate the effects of yohimbine on medetomidine sedation. Twenty dogs were sedated with medetomidine(0.04mg/kg, IM). Twen쇼 minutes after the injection, ten dogs were injected with saline(0.1mg/, IV)for the control group and the others were injected wi yohimbine(0.1mg/kg, IV)for the experimental group. Onset, recovery time, respiratory rate, body temperature, blood chemistry, electrocardiogram(ECG) finding were recorded. The results obtained were summarized as follows; 1. Onset of the sedation was fast and favorable. 2. Recovery time was shorted significantly by yohimbine treatment(p<0.01). 3. Respiratory rates were decreased significantly, but increased to normal level after the yohimblne treatment(p<0.01). 4. Heart rates were decreased significantly; but increased to normal level after the yohimbine treatment(p<0.01). 5. Body temperatures of dogs in the experimental group revealed higher level than those of control group(p<0.01). 6. Arrythmias were observed in both groups but relieved to normal after the yohimbine treatment. 7. Blood chemistry values were not changed significantly by medetomidine and yohimbine treatment. 8. These results showed that yohimbine is an excellent antagonist of medetomidine.