To compare efficacy and cardiorespiratory effects of dexmedetomidine and tiletamine in combination with butorphanol, morphine, or buprenorphine (with or without reversal by atipamezole) in dogs undergoing castration. Design - prospective, randomized, split-plot, blinded study. Animals - 30 healthy, client-owned, sexually intact male dogs. Procedures - dogs (n = 10 dogs/group) were assigned to receive dexmedetomidine (15 µg/kg [6.82 µg/lb]) and tiletamine (3 mg/kg [1.36 mg/lb]) with butorphanol (0.2 mg/kg [0.09 mg/lb]; DTBut), the same dosages of dexmedetomidine and tiletamine with morphine (0.05 mg/kg [0.023 mg/lb]; DTM), or the same dosages of dexmedetomidine and tiletamine with buprenorphine (40 µg/kg [18.18 µg/lb]; DTBup). All drugs were administered as a single IM injection for induction and maintenance of anesthesia for castration.