AIM: To assess the impact of procollagen Ⅲ peptide as a marker of collagenesis in the development of pseudopolyps in patients with ulcerative colitis.METHODS: Development of pseudopolyps was monitored in 25 patients with ulcerative colitis classified according to Powell-Tuck index as mild (n=12) or moderate (n=13) form of disease. Patients with a mild form of disease were treated with oral mesalazine medication (2-4 g/day) and local mesalazine preparation (suppository). Patients with a moderate form of disease oral mesalazine medication (2-4 g/day), local mesalazine preparation (suppository) and local methylprednisolone at an initial dose of 60 mg/day, followed by dose tapering. How many significant variables (previously determined by analysis of variance) were elevated in the groups with and without pseudopolyp developement was observed. ROC analysis for calculation of new index was made.RESULTS: Serum values of procollagen Ⅲ peptide (PⅢP), Creactive protein (CRP) and C4 complement component (C4)were statistically significantly lower in the group of patients free from pseudopolyp development than those who developed one or more pseudopolyps (0.45±0.12 vs 1.42±0.70,P＜0.0027; 7.6±4.7 vs 17.8±9.17, P＜0.035; and 0.46±0.11rs0.34±0.16, P＜0.068, respectively) at endoscopic conrtrols with patohistologically samples during 13 months. There were no statistically significant differences in the values of C3, ceruloplasmin and IgM between the two groups (P＞0.05).Discrimination function analysis yielded highest standardized cannon coefficients for PⅢP (0.876), CRP (0.104), C3 (-0.534)and C4 (0.184) (P＜0.036). The elevation in two of three laboratory variables (PⅢP, CRP and C4) reached sensitivity of 93 % and specificity of 90 % in the development of pseudopolyps.CONCLUSION: It is proposed that an increase in two of the three laboratory parameters (PⅢP, CRP and C4) could improve the accuracy of prediction of the development of pseudopolyps. When using PⅢP, CRP and C4 on decision making, the positive predictive value and accuracy were 90 %and 92 %, respectively.