Thirty five adult crabeater seals (Lobodon carcinophaga) were anesthetized with combinations of the sedative midazolam and the gaseous anesthetic isoflurane during three research cruises to the Antarctic Peninsula (∼67°S, 67°W) in the austral winters of 2001 and 2002. Modifications were required to gas anesthetic equipment to achieve field portability and sufficient heating to allow operations in temperatures as low as -20°C. Seals were sedated with an average intramuscular dose of midazolam of 0.55 ± 0.14 mg/kg delivered via a pole syringe (n= 32). One seal was not given midazolam and two seals were injected intravenously. Premedication with midazolam provided moderate sedation, making capture and masking practical and safe. Mean induction time with isoflurane was 8 ± 4.8 min. Mean maintenance concentration over the anesthetic period were 2.3%± 0.9% of isoflurane. Average recovery time was 18.2 ± 8.8 min. No substantial difficulties were experienced and anesthetics were easily managed. This drug combination and the use of modified, heated equipment provide an effective anesthetic procedure for crabeater seals.