1. A series of 188 cases investigated and followed up is described and tabulated. Of these, 151 were cases of suspected intestinal obstruction, and 37 cases of post-operative distension.2. Relevant anatomical and physiological features are discussed and normal radiological appearances described. Pathological features of intestinal obstruction are mentioned and for the purposes of this paper obstructions are classified as mechanical and adynamic (or neurogenic) obstructions.3. A routine technique of a supine and an erect radiograph of the abdomen using a postero-anterior projection where possible, and using intensifying screens and a moving grid at an anode-film distance of 36 to 48 inches, is recommended. Techniques for difficult cases are mentioned.4. The appearances of mechanical obstruction of the bowel are (a) stasis within the bowel as shown by the presence of fluid levels, and (b) distension of bowel by gas.5. The site of the obstruction can be localised as being distal to the most distal part of distended bowel. Thus small bowel obstructions can be labelled high, mid or low small bowel obstructions. Large bowel obstructions can usually be localised more accurately; care must be taken not to diagnose a large bowel obstruction with an incompetent ileo-cæcal valve as a small bowel obstruction.6. Certain radiological appearances which are diagnostic of acute obstructions are described and the use of the Miller-Abbott tube is discussed.7. Other conditions which may produce radiological signs, recognisable on scout survey films, such as volvulus, intussusception and perforation of a gas-containing viscus, are described.8. Negative X-ray findings must be evaluated with reserve. Mechanical obstruction may still exist in the absence of positive radiological evidence.9. The appearances of adynamic obstruction, localised and generalised, are described. It is of the utmost importance to differentiate between this type and mechanical obstructions as the early recognition of the latter in post-operative cases may be a life-saving measure.10. Assessment of a deficient properitoneal line is discussed and the consideration of technical factors in this respect stressed. The radiological appearances of intraperitoneal fluid are described.11. Finally the extreme importance of close liaison between radiologist and clinician is emphasised.