The harp seal (Pagophilus groenlandicus) was anesthetized with halothane following induction with halothane/nitrous oxide or thiopental sodium. Halothane concentrations of 0.75 - 1.5% were required for surgical anesthesia. The depth of anesthesia was best assessed by heart rate, muscle relaxation and the presence or absence of shivering. Controlled ventilation was required throughout anesthesia and CO₂ homeostasis was maintained by tidal volumes of 22–25 ml/kg at a rate of 10/min. There were two anesthetic deaths: one related to hypothermia, and one to a prolonged induction period.