Alpha-1-proteinase inhibitor-bound elastase (EPIC) was measured in plasma and fresh stool samples from 20 patients with Crohn's disease (CD), 16 patients with ulcerative colitis (UC), and 10 controls. Median EPIC values were significantly higher than normal in active CD and UC. EPIC was virtually undetectable in the stool samples of control subjects. Median faecal EPIC in 14 patients with active CD (478 ng/ml) or 10 patients with active UC (1159 ng/ml) was significantly higher than in quiescent disease (p less than 0.05) and in control subjects (p less than 0.001 in each case). The difference in the median values between active CD and UC was not significant (p = 0.065). The median faecal EPIC levels were identical in active UC (1159 ng/ml) and patients with large-bowel CD (LBCD) (1015 ng/ml) (p = 0.9), and each was significantly higher than the value of 168 ng/ml in small-bowel CD (SBCD) (p less than 0.01 in each case). In active LBCD but not in SBCD, faecal EPIC correlated significantly with Crohn's disease activity index (R = 0.78, p less than 0.05), plasma C-reactive protein (CRP) (R = 0.9, p less than 0.01), and erythrocyte sedimentation rate (ESR) (R = 0.74, p less than 0.05). In active UC, faecal EPIC correlated significantly with a numerical disease activity index (R = 0.9, p less than 0.01) but not with plasma EPIC and CRP, ESR, and leucocyte counts. Faecal EPIC values may be a better reflection of disease activity in active UC than plasma levels of markers of inflammation.