Abstract THE cystic structure commonly termed a “breast blister” occurs very frequently on the ventral aspect of the sternal crest of chickens and turkeys. A high incidence of breast blisters at slaughter was reported by DeCamp (1956). Second rank after bruises was given by Crothers and Helbacka (1960) in a study of causes of down grading and condemnations in broilers. The development of the “breast blister” was partially outlined by Hodgson and Gutteridge (1941). The structure was absent in this study at one day of age. Later growth of spongy tissue under the skin preceeded formation of a large “blister” containing fluid resembling egg white. After more detailed study, O’Neil (1943) reported a true bursa which was tentatively termed “the bursa synovalis presternalis.” An enlargement of this structure was considered as a noninfectious bursitis. Gresham and Barwick (1962) described the sac as lined by pink fleshy folds. Histologically the synovial folds . . .