During a study of planulation in the central region of the Great Barrier Reef [Australia] the coral Seriatopora hystrix Dana exhibited an escape response to environmental stress. This response, which occurs relatively rapidly, is termed polyp bail-out. It proceeded in 3 steps: isolation of individual polyps via the polyp-ward movement of coenosarc; emergence of polyps and detachment from the skeleton; and dispersal, re-attachment to the bottom, and secretion of a new skeleton. Of the 250 polyps observed .ltoreq. 5% successfully settled and secreted skeletons within 7 to 9 d [days] under laboratory conditions. Polyps retained zooxanthellae during the process and usually possessed 2 slightly adhesive filaments which may have assisted in re-attachment. Bail-out may be induced at any time in the laboratory and occurred naturally in the field on several occasions. The peak period of planulation for S. hystrix was Nov. (early summer, Southern Hemisphere). During the normal spawning period, some polyps detached themselves while carrying active planulae. These polyps later disintegrated, releasing the larvae which settled normally. Bail-out may be 1 factor contributing to dominance of this species within certain reef habitats. This process of isolation and detachment of individuals from a coral followed by dispersal, re-settlement, and re-initiation of skeletogenesis probably represented a previously unknown mode of asexual reproduction in the Scleractinia.