We evaluated the serum transglutaminase activity in patients with inflammatory bowel diseases (IBD) to correlate its level with clinical status. There were 49 patients with Crohn's disease (CD), 50 with ulcerative colitis (UC), 35 with diseases other than IBD as control group and 42 healthy subjects matched for sex and age. Enzyme activity was significantly lower in both IBD groups than in controls and in normal subjects (p less than 0.001); we found a significant negative correlation between serum transglutaminase (TG) activity and clinical severity of the disease in both IBD patient groups (r = -0.54 in CD, and r = -0.69 in UC). Moreover, in UC and CD patients, a serum TG value lower than 0.80 mU/ml retrospectively proved to predict the need for major surgery and/or total parenteral nutrition. These results suggest that serum TG may prove useful in the management of inflammatory intestinal diseases in predicting clinical outcome.