Neutrophil superoxide anion production was measured in healthy subjects and in patients with quiescent and active Crohn's disease using superoxide dismutase inhibitable cytochrome C reduction. Three stimuli were used: phorbol 12-myristate 13-acetate (PMA1), phorbol 20-oxo-20-deoxy 12-myristate 13-acetate (PMA2), and Candida albicans in serum. Normal neutrophils produced significantly more superoxide anion than Crohn's disease neutrophils with both PMA1 (mean (SD) 9.6 (2.2) v 8.6 (1.8) nmol/10(6) cells/5 minutes, p = 0.04) and PMA2 (1.8 (0.8) v 0.8 (0.77) nmol/10(6) cells/5 minutes, p = 0.00004). With C albicans in serum, normal and Crohn's disease neutrophils produced similar amounts of superoxide anion (4.4 (1.5) v 4.3 (1.7) nmol/10(6) cells/30 minutes, not significant). Results were independent of disease activity. Superoxide anion production by PMA-stimulated Crohn's disease neutrophils is significantly lower than by normal neutrophils.