Xylazine hydrochloride was used to immobilize 124 Rocky Mountain bighorn sheep (Ovis canadensis canadensis) between 1983 and 1988. Doses of xylazine for free-ranging lambs ranged from 70 to 130 mg with amounts increasing with lamb age. Average doses for 11 free-ranging adult males and 21 adult females darted from the ground were (x̄ ± SE) 363 ± 16 and 251 ± 7 mg, respectively. Adult females captured in “Stevenson's” box traps (n = 7) could be immobilized with significantly (P < 0.001) less xylazine (93 ± 9 mg) than free-ranging females but had similar induction times. Long recovery times associated with xylazine immobilization were eliminated with the intravenous administration of idazoxan (RX 781094) at an approximate dosage of 0.1 mg/kg. Eighteen sheep given idazoxan appeared fully recovered within 3 min of injection (x̄ ± SE = 1.2 ± 0.2 min). Four mortalities (three lambs, one yearling male) (3% of total) occurred before idazoxan was available for trial.