Fourteen wolves (Canis lupus L.) were singularly or repeatedly immobilized with 30 mg xylazine hydrochloride (HCl) and 400 mg ketamine HCl. Mean induction time was 5.3 +/- 4.6 min (mean +/- SD). Administration of 8.0 mg/kg tolazoline HCl as an antagonist significantly reduced immobilization times from 148.0 +/- 52.7 to 47.9 +/- 8.9 min (F = 63.69, df = 1,17, P less than 0.05). The average times from injection to ambulation for 2.0, 4.0, and 8.0 mg/kg tolazoline HCl were 35.2 +/- 31.8, 18.5 +/- 11.7, and 10.2 +/- 9.1 min. Tolazoline HCl increased heart rates significantly (P less than 0.001) from 75 +/- 14 to 120 +/- 23 beats/min, reversing a xylazine HCl-induced bradycardia. Respiratory rates also increased significantly (P less than 0.01) after tolazoline HCl injection from 19 +/- 7 to 28 +/- 8 breaths/min. Immobilization resulted in an initial hypertension which was normalized after tolazoline HCl administration. One female wolf had a single sinoatrial block within 1 min of receiving tolazoline HCl. Tolazoline HCl appears to be an effective antagonist for xylazine HCl-ketamine HCl immobilization of wolves.