Significantly decreased levels of serumcholinesterase (CHE) were found in acute Crohn's disease (= CD) (3.2 +/- 1.0 KU/L) and acute ulcerative colitis (= UC) (3.54 +/- 1.6 KU/L) as compared to patients with mild or quiescient disease (CD: 5.5 +/- 1.1 KU/L; UC: 5.59 +/- 0.94 KU/L) and healthy controls (5.69 +/- 1.3 KU/L). Suppression of CHE was most evident in Crohn's colitis (2.98 +/- 1.0 KU/L) and extensive UC (2.96 +/- 1.28 KU/L). Intraindividual comparison showed an increase of CHE-levels during treatment with steroids and salicylates. There was no significant correlation to the reduced bodyweight-levels in severe IBD. Best correlations were seen between CHE/albumin (CD: r = +0.61; UC: r = +0.73) and CHE/hematocrit (CD: r = +0.50; UC: r = +0.61) in severe inflammatory bowel disease. The results of a discriminant analysis showed that CHE-levels can predict the degree of activity correctly in the majority of patients with CD and UC. It is suggested that the decrease of serumcholinesterase reflects an inhibition of liver synthesis as an acute phase response-induced by endotoxins and cytokines.