This population-based cohort shows marked changes in rates of surgery, and the reduction is independently associated with year of diagnosis, and associated temporally with increased and earlier thiopurine use.

The thickness of adherent mucus gel on the surface of colonic mucosa was measured in surgically resected specimens from 46 'control' patients most of whom had carcinoma of the colon; 12 were from right colon, 17 left colon, and 21 from rectum. In addition specimens were examined from 17 patients with ulcerative colitis and 15 patients with Crohn's disease. In controls a continuous layer of mucus was readily seen on specially prepared sections viewed by phase contrast illumination. Mean values for right and left colon and rectum were 107 (48), 134 (68), and 155 (54) ,tm respectively with a significant difference between right colon and rectum (p=0015). Values in ulcerative colitis showed greater variation and in those areas with acute inflammation mucosa was denuded of the mucus layer. In contrast, values for Crohn's disease were normal or greater than normal in thickness -right colon 190 (83) [tm compared with 107 48 ,um, p=0-0093. A series of validation experiments are described for the method used to measure mucus thickness. The possible role of mucus in the pathogenesis of inflammatory bowel disease is discussed.

115-4 (21-9), n=15) were not different to control results. Eight patients had carcinomas (rectal (2), sigmoid (4), and caecal (2)) all of which were adenocarcinomas. The cancers (193.6 (40.2), n=8) synthesised more PGE2 than control specimens (p<0001), but were not different to polyps. Cancerassociated mucosa (140.3 (27.7) n=8) synthesised more PGE2 than control and polypassociated mucosa. Colorectal neoplasia is associated with a progressive increase in PGE2 synthesis which may have a role in tumourigenesis and be a pathophysiological explanation for the beneficial effects of NSAIDs in animal models and human disease.

Transdermal nicotine alone was no better than placebo in the maintenance of remission of ulcerative colitis, and premature withdrawal due to side effects was more common in the nicotine group.