Features of the neutrophil oxidative metabolism and enzyme activity in peripheral blood neutrophils were studied in 43 patients with Crohn's disease, 13 with ulcerative colitis and 33 healthy controls. The production of superoxide anion (O2-.) by phorbol-myristate-acetate stimulated neutrophils from patients with Crohn's disease and ulcerative colitis was significantly diminished compared with controls mean (SE) = 47.1 (3.6) and 38.0 (3.8) v 67.4 (7.5) nmol/10(7) cells/min, p less than or equal to 0.02, respectively, while the production of hydrogen peroxide was normal. The neutrophil content of superoxide dismutase (SOD), a cytoprotective enzyme, was also markedly diminished in Crohn's disease mean (SE) = 7.11 (0.23) ng SOD/micrograms DNA, p less than 0.05, and ulcerative colitis mean (SE) = 5.74 (0.42) compared with controls 7.84 (0.27), p less than 0.001. In contrast, the concentration of neutrophil elastase, a neutral protease, was found to be normal when compared with neutrophils from controls. The neutrophil O2-. production and the SOD concentrations were significantly and negatively correlated with the disease activity in Crohn's disease and ulcerative colitis. The results indicate diminished neutrophil function in peripheral blood of patients with Crohn's disease and ulcerative colitis as illustrated by a diminished oxidative system, which correlates with the disease activity.