Neutrophils from asthmatic patients seem to be in an activated state. This study demonstrated that superoxide radical (O2-) production was enhanced in asthmatic patients compared with healthy control subjects. Production of (O2-) also increased with progression of disease and with disease duration. In addition, (O2-) release was inversely correlated with FEV1 and midflows and was greater in neutrophils from patients with exacerbated disease than in those from patients with stable disease. These findings suggest that oxygen metabolites may play a direct or indirect role in the modulation of airway inflammation.