['Physical performance measured by gait speed is being recognized as a major instrument for clinical evaluation in older adults, because it predicts physical frailty, loss of autonomy, hospitalization and decreased survival. Low-grade chronic inflammation and oxidative stress, mediated partly by the superoxide anion produced by NADPH oxidase, are closely linked and could be involved in age-related physical decline.', 'To determine whether slow gait speed is associated with superoxide anion overproduction by NADPH oxidase and low-grade chronic inflammation.', 'Observational study among the 280 elderly of an ambulatory geriatric care unit (191 women, 89 men, 79.9 ± 6.1 years old).', 'Gait speed was evaluated by walking at self-chosen usual pace. Usual gait speed < 0.8 m/s was defined as slow gait speed. Superoxide anion production was evaluated using a lucigenin-based chemiluminescence method. Inflammation was evaluated by CRP, fibrinogen and leukocyte count.', 'Among the 280 participants, 179 (63.9%) walked with a gait speed < 0.8 m/s (slow walkers) and 101 (36.1%) with a gait speed ≥ 0.8 m/s. Superoxide production and inflammation markers, such as fibrinogen, were more important in slow walkers (p = 0.004 and p = 0.006, respectively). In multivariate analysis, superoxide anion overproduction and fibrinogen were independently associated with physical frailty assessed by slow gait speed (p = 0.028 and p = 0.007, respectively).'] Are low-grade chronic inflammation and superoxide anion production by NADPH oxidase the main determinants of physical frailty in older adults?