PMN-elastase is a proteinase released by activated neutrophils. PMN-elastase was determined in two independent populations with inflammatory bowel disease. In an unselected population of 70 consecutive patients with Crohn's disease and 24 patients with ulcerative colitis with different degrees of disease activity plasma PMN-elastase levels were statistically significantly higher in patients with active than in patients with inactive disease [Crohn's disease: 80.5 +/- 33.2 ng/ml vs 60.1 +/- 24.6 ng/ml (mean +/- SD), P = 0.0017; ulcerative colitis: 98.2 +/- 54.9 ng/ml vs 59.2 +/- 16.8 ng/ml, P = 0.026]. PMN-elastase levels in feces were also higher in patients with active Crohn's disease (23.6 +/- 15.3 ng/g vs 13.6 +/- 12.5 ng/g, P = 0.0021) and active ulcerative colitis (46.5 +/- 60.5 ng/g vs 20.2 +/- 25.0 ng/g, P = 0.46), but the difference reached significance only in Crohn's disease. Correlation of disease activity and PMN-elastase in individual patients showed a statistically significant correlation between plasma and fecal elastase concentrations and disease activity in ulcerative colitis (plasma: r = 0.72, P < 0.001; feces: r = 0.57, P = 0.002). In patients with Crohn's disease only plasma levels of PMN-elastase (r = 0.423, P < 0.001) but not fecal elastase concentrations (r = 0.0083, P = 0.485) correlated significantly with disease activity. Plasma PMN-elastase correlated weakly with fecal PMN-elastase levels in Crohn's disease (r = 0.431, P < 0.01) and in ulcerative colitis (r = 0.515, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)