The aim of this study is to investigate the accuracy of serum matrix metalloproteinase (MMP) levels in an effort to find a reliable factor that may play an important role in pathogenesis of hemorrhoidal disease. Twenty control subjects and 21 Grade I, 19 Grade II, 20 Grade III, and 21 Grade IV patients with internal hemorrhoid were included in this prospective study. The mean ages of control subjects were 47.65 +/- 6.71 standard deviation (SD) years (range, 37 to 60 years). The mean age of internal Grade I, Grade II, Grade III, and Grade IV patients with internal hemorrhoid were 48.85 +/- 6.44, 47.20 +/- 6.75, 44.90 +/- 6.13, and 42.95 +/- 3.49 SD years (ranges, 38 to 58, 38 to 60, 34 to 55, and 38 to 50 years), respectively. Ten milliliters of blood was taken from all subjects. Enzymelinked immunosorbent assay (ELISA) for MMP-1, -2, -7, and -9 levels were performed using an ELISA kit (R&D Systems) following the manufacturer's instructions. There was an important difference between Grade I and Grade II groups in the serum levels of MMP-9 (P <0.01). Patients with Grade III hemorrhoidal disease had significantly higher serum levels of all MMP than patients with Grade I and Grade II hemorrhoidal disease (P < 0.001). Also, patients with Grade 4 hemorrhoidal disease had higher serum levels of MMP-7 and -9 according to Grade I, II, and III groups (P < 0.01, 0.001). High serum levels of MMP are present in patients with hemorrhoids, suggesting the possible mechanism in the pathogenesis of hemorrhoids.