Recent work has shown that the most common abnormality on screening of immune function in cohort of adult subjects with bronchiectasis was a low neutrophil oxidative burst. To assess the functional significance of a low oxidative burst in subjects with idiopathic bronchiectasis. Neutrophils with a low oxidative burst were obtained from six bronchiectasis patients and assessed for their ability to kill Staphylococcus aureus. The results were compared with those obtained using neutrophils from 12 healthy controls subjects and control neutrophils treated with dimethylthiourea (DMTU), an inhibitor of the oxidative burst. The results showed that the bronchiectasis subjects had significantly reduced killing of bacteria compared with controls (po0.001). The addition of DMTU to neutrophils of control subjects significantly impaired both the oxidative burst and bactericidal activity. The addition of interferon-g enhanced oxidative burst in both groups. Abnormal neutrophil function in some subjects with bronchiectasis may account for their high rate of infection.