The cardiovascular and pulmonary effects of tiletamine/ zolazepam, propofol and tiletamine/zolazepam plus propofol were studied in five mongrel dogs. A cannula inserted into a raised carotid artery was used to measure mean arterial pressure (MAP) and heart rate continuously and to collect arterial blood for the determination of pH, PO2, PCO2, bicarbonate and base balance. Respiratory frequency and rectal temperature were also recorded. In the two propofol groups premedication had no significant effect on the time to rejection of an endotracheal tube and the return to sternal recumbency. The MAP and heart rate increased after tiletamine/zolazepam alone and after tiletamine/zolazepam plus propofol, although propofol alone reduced MAP and transiently increased heart rate. Respiratory frequency decreased transiently in both propofol groups in association with a significant increase in PaCO2 and decrease in PaO2. The most notable change was the hypoxaemia in the tiletamine/zolazepam plus propofol group in which the PaO2 was reduced. In all the dogs given tiletamine/ zolazepam alone undesirable side effects were observed, effects which also occurred during the recovery of the dogs given tiletamine/zolazepam plus propofol.