This study evaluated the quality of anaesthesia and the cardiorespiratory effects induced by the combination of medetomidine with either ketamine, propofol or fentanyl. Medetomidine premedication (1000 or 1500 micrograms/m2 body surface area) was followed by intravenous induction of anaesthesia with ketamine (3.0 mg/kg), propofol (2.0 mg/kg) or fentanyl (2.0 micrograms/kg) in bitches undergoing elective ovariohysterectomy. Anaesthesia was prolonged by incremental doses of the induction agents as necessary. The mean (sem) overall doses (including induction) were 0.09 (0.01) mg/kg/min for ketamine, 0.06 (0.01) mg/kg/min for propofol and 0.07 (0.005) microgram/kg/min for fentanyl during procedures which lasted 88 (6) minutes, 72 (3) minutes and 79 (7) minutes, respectively. At the end of the procedure, medetomidine was antagonised with atipamezole. The quality of anaesthesia, heart rate and arterial blood pressure were recorded continuously and arterial blood gases were measured at intervals. At the end of the procedure, the animals received 10 micrograms/kg buprenorphine intramuscularly for postoperative analgesia. From the adequacy of anaesthesia, the lack of significant adverse side effects and the reliable and rapid recovery it is concluded that, in healthy dogs anaesthetised with ketamine or propofol, medetomidine is a satisfactory sedative-analgesic premedicant. The differences in haemodynamics and the quality of recovery suggest that the combination of medetomidine with propofol provided the better quality anaesthesia. The combination of medetomidine with fentanyl was unsuitable for obtaining surgical anaesthesia in spontaneously breathing animals owing to the severity of the respiratory depression at dosages needed for general anaesthesia.