Combinations of medetomidine with either propofol or ketamine were compared for the sedation and induction of anaesthesia in dogs undergoing a variety of surgical (60 per cent) and non.surgical (40 per cent) procedures. Eighty.four dogs were used at four sites. Medetomidine was administered intramuscularly at a dose of 1000 μg/m2 body surface area 10 to 15 minutes before the induction of anaesthesia by the administration of propofol (n = 44) or ketamine (n = 40) dosed to effect. The dogs became sedated by medetomidine after a mean (sd) time of 6.7 (5.4) minutes, and their heart rates and respiration rates decreased. Sixteen of the dogs suffered an adverse effect, 13 of them vomited. Anaesthesia was induced by the intravenous administration of propofol (2.1 [0.7] mg/kg) or ketamine (3.7 [1.9] mg/kg), and further doses of the anaesthetic were given, depending on the length of the operation, once in 17 per cent, twice in 11 per cent and three or more times in 24 per cent of the cases. The heart rate of the dogs anaesthetised with ketamine was significantly higher than that of the dogs anaesthetised with propofol, but there were no other significant physiological differences. There were 11 adverse side.effects in the ketamine group compared with five in the propofol group and they were generally more severe. The quality of the recovery from anaesthesia was considered to be smooth in 89 per cent of the propofol group but in only 63 per cent of the ketamine group.