The cardiopulmonary effects of three drug combinations in polar bears (Ursus maritimus) were studied. In 1995, five adult polar bears received i.m. injections of either 8.2 +/- 1.3 mg/kg of Telazol or a combination of 159 +/- 34 microg/kg of medetomidine with 4 +/- 0.8 mg/kg of ketamine in a crossover design. Significantly higher mean arterial pressure, lower heart rate, and lower partial pressure of arterial oxygen (Pao2) occurred with medetomidine-ketamine. In 1996, six adult polar bears were immobilized with i.m. injections of either 8.2 +/- 2 mg/kg of zolazepam-tiletamine or a combination of 74.8 +/- 11.8 microg/kg of medetomidine plus 2.2 +/- 0.3 mg/kg of zolazepam-tiletamine in a crossover design. Significantly higher mean arterial pressure and lower heart rate, base excess, and Pao2 occurred with medetomidine-zolazepam-tiletamine compared with zolazepam-tiletamine alone. Hypertension, bradycardia, and decreased Pao2 were observed with both medetomidine-ketamine and medetomidine-zolazepam-tiletamine. Both combinations should be well tolerated by healthy bears, but both have the potential to produce adverse effects in animals with cardiopulmonary disease. Zolazepam-tiletamine produced minimal adverse cardiopulmonary effects, consistent with the wide margin of safety of this combination in bears. The analgesic effect of zolazepam-tiletamine was apparently poor on the basis of the marked increases in pulse rate and mean arterial pressure after noxious stimuli.