In 1994, an experimental longline fishery for hake Merluccius spp. commenced in the shelf waters off South Africa. Participants were required to record any birds caught, and these data were supplemented by ship-based observers on several vessels. Longlines are set at night, and the white-chinned petrel Procellaria aequinoctialis was the only seabird species caught while attempting to scavenge bait during gear setting. Small numbers of great shearwaters Puffinus gravis and pintado petrels Daption capense were killed during hauling operations. The hake longline fishery is estimated to kill 8000 ± 6400 white-chinned petrels a year in South African waters at a rate of 0.44 birds per 1000 hooks. This represents < 1% of the global white-chinned petrel population, but is cause for concern given (1) the slow reproductive rate among procellariiform seabirds; (2) the projected growth in the longline hake fishery; and (3) the increasing numbers of white-chinned petrels being killed in other longline fisheries. Light intensity was the most important factor for explaining variation in the number of petrels caught during setting; when line shooting was completed prior to the increase in white-chinned petrel activity (c. 2·5 h before sunrise), few birds were caught. Measures to reduce excessive seabird bycatch include: (1) the introduction of bird lines on all vessels; (2) restricting the setting of lines to times of least bird activity; (3) minimum use of deck lighting during setting; and (4) ensuring that baited hooks sink as fast as possible when deployed. Hauling mortalities can be reduced by diverting offal outlets to the opposite side of the vessel to where the longline is being hauled. Keywords: Longline fishing, bycatch, seabirds, white-chinned petrels, Procellaria.