From the Gastrointestinal Unit and Departments of Clinical Surgery and Medicine, University ofEdinburgh and Western General Hospital, Edinburgh

SUMMARY Balloon distension of the distal colon in diverticular disease does not produce the, pressure change in response to increasing volumes that occurs in normal subjects. This phenom-enon, though modified at first by resection, is not abolished by resection nor by myotomy or bran. This adaptive quality of the wall of the colon to balloon distension possibly reflects a structural change in its wall, as the phenomenon was present in the colon in diverticular disease in vitro as well as in vivo. The muscle of the large intestine is capable of producing a raised intraluminal pressure in diver-ticular disease. ' 2 The force created may have a critical role in extruding the diverticulum. Further-more, the reduction of the pressure appears to be beneficial in that symptoms become less and com-plications may become fewer.3 A paradox exists, however, in that balloon distension of the colon in diverticular disease4 produces a prematur