The cardiorespiratory and analgesic effects of romifidine or xylazine combined with ketamine was investigated in dogs. Dogs were premedicated with 1.0 mg/kg of methotrimeprazine IV, followed by 0.1 mg/kg of romifidine (n = 8) or 1.0 mg/kg of xylazine (n = 8) and 15 mg/kg of ketamine IM, using a double blind randomised design. Dogs of both groups developed hypothermia, bradycardia, slight hypotension and reduction in respiratory rate and minute volume. There were minimal changes in end tidal CO2 and O2 saturation. There were no differences either in time or between the groups in pH, PaO2, and blood biochemistry. The reflexes to pain were reduced until 30-45 minutes of anaesthesia in both groups. Twelve bitches were divided in two groups as above and underwent ovariohysterectomy. Recovery was longer after romifidine/ketamine when compared to xylazine/ketamine in both studies. Although these anaesthetic protocols produced minimal cardiorespiratory changes, the quality of anaesthesia was not ideal for ovariohysterectomy