This paper seeks to correct the widely held belief that a clinical or bacteriological diagnosis of infective diarrhoea excludes the presence or development of acute appendicitis. The work that is described was stimulated by isolated incidents that occurred between 1950-1955: these are summarized in Table 1. In that period nine children had appendicectomies either when a bowel infection was present or before such an infection became manifest in the post-operative period: at operation four out of these nine cases were found to have acute appendicitis. A preliminary communication on the thesis of this paper was read at this hospital at a Summer meeting of the Paediatric Section of the Royal Society of Medicine in 1957 (Rogers, 1957). Because of the findings shown in Table 1 an investigation was organized to inquire into the role of bowel infection as a factor in the aetiology of acute appendicitis: it was quite fortuitous that our planned project was started in January 1956, when a pandemic of Sonne dysentery in England was beginning.