We have previously shown that the percentage distribution of the pseudocholinesterase isozymes (C1, C2, C3 and C4) is significantly altered in patients with active Crohn’s disease (CD). The aim of the present study was to assess the time course and the clinical meaning of the pseudocholinesterase isozymes during an acute phase in CD. Ten healthy volunteers and 10 patients with active CD (Crohn’s disease activity index, CDAI, > 200) were examined. In CD patients an acute phase treatment with prednisolone was administered for 7 weeks reaching an improvement (CDAI < 200) in 7 patients. Before initiation of steroid treatment, the isozymes C1 (controls: median 19.7%, interquartile range 16-22.2%; CD: 6.2%, 5-8%; p < 0.001) and C4 (controls: 63.5%, 59-71%; CD 81.7%, 72.9-84.7%; p < 0.001) were decreased and increased, respectively, and did not change significantly during the time of acute phase treatment. The isozymes C2 and C3 did not show any difference between controls and CD patients. Five of the patients were followed up for the subsequent 3 months of remission (CDAI < 150). During this period C1 and C4 normalized and no difference between controls and CD patients was obtained (C1: 16.4%, 15.5-20.2%; C4: 59.4%, 55.8-60.5%). Therefore, pseudocholinesterase isozymes are useful parameters in CD to indicate active CD or long-term remiss