Crohn's disease (CD) is a chronic inflammatory bowel disease of still unknown etiology. The aim of our study was to find out whether there are any changes in the colonic wall of CD patients that could give hints for a predisposing disorder concerning the extracellular matrix, especially the collagen metabolism. Eight samples of colonic tissue from patients with Crohn's disease were compared to 14 specimens from patients without Crohn's disease. We performed a sirius red test for the overall collagen content and immunohistochemical studies examining differentiation between" collagen type I and type III and the expression of MMP-1 and MMP-13. In the bowel sections of patients with Crohn's disease, decreased levels of mature collagen type I with a resulting lower ratio of collagen I/III compared to patients without Crohn's disease were found (1.12 +/- 0.29 vs. 1.59 i 0.31). The expression of MMP-1 was significantly increased in the CD group (9.21 i 6.02 vs.6.02 i 1.98), whereas expression of MMP-13 showed no difference in both groups. Our study gives the first indication that preexisting changes of the extracellular matrix in the colonic wall may play a role in the pathogenesis of CD. Further studies have to be done to elucidate these interesting aspect of the pathogenesis in Crohn's disease.