Longlining operations for Dissostichus eleginoides off South Georgia were assessed for interactions with seabirds and the effectiveness of measures employed by CCAMLR to mitigate seabird mortality. Following an agreement between the Governments of the United Kingdom and Chile, a UK observer was placed aboard a Chilean longliner, the BF Cisne Verde, fishing in CCAMLR Subarea 48.3 during the 1996/97 season. In this study 61 lines were laid from March to May 1997 using the Spanish double-line method. In accordance with CCAMLR conservation measures, lines were set at night, weights (6-7 kg) were set at 50 m intervals along the line, all deck lights were extinguished and no offal was discarded during setting. A streamer line made to CCAMLR specifications was also used, except during an experiment that attempted to assess the effectiveness of the streamer line in mitigating incidental mortality of seabirds during night-time setting. Data were recorded during hauling using a randomised cluster sampling method, developed to allow representative data to be collected when 100% observer coverage could not be achieved: A total of 12 dead seabirds were recorded, giving an average mortality rate/night of 0.099 birds/l 000 observed hooks, substantially lower than other vessels fishing around South Georgia during the same period. Mortalities consisted of nine white-chinned petrels, two black-browed albatrosses and one unidentifiable bird caught on hooks. One giant petrel was also killed as a result of flying into the side of the vessel. Generally, few birds were seen following the vessel during setting operations. During April, however, large numbers of white-chinned petrels were seen occasionally, and large numbers of black-browed albatrosses were seen when the moon was full. Live birds were observed to become caught on hooks during hauling on 23 occasions; all birds were released alive. Black-browed albatrosses concentrated on taking returning bait off the line and accounted for 18 birds caught; giant petrels concentrated on taking discarded offal, and accounted for five birds caught.