Serum CEA was measured in 78 patients with chronic inflammatory bowel disease. One of 17 patients with ulcerative proctitis, 3 of 30 with ulcerative colitis and 4 of 31 with Crohn’s disease had elevated serum levels of CEA. All patients with increased levels had symptomatic disease. There was no evidence for the presence of carcinoma of the colon in these patients. It is unlikely that single measurements of serum CEA by presently available tests will be of value as a screening procedure for early carcinoma of thecolon in the presence of chronic inflammatory bowel diseas