In heaves-affected horses the relation between oxidant status, airway inflammation (AI) and pulmonary function (PF) is unknown. The oxidant status of blood and pulmonary epithelial lining fluid (PELF) of healthy (H, n = 6) and heaves-affected horses in clinical remission (REM, n = 6) and in crisis (CR, n = 7) was assessed at rest, during and afterstandardised exercise test by measurement of reduced and oxidised glutathione, glutathione redox ratio [GRR%]; uric acid and 8-epi-PGF2α. Oxidant status was related to PF parameters (mechanics of breathing and arterial blood gas tension) and AI parameters (bronchoalveolar lavage [BAL] neutrophil% and AI score). Haemolysate glutathione was significantly different between groups and was correlated with PF and AI parameters; GRR in PELF was increased during CR and was correlated with PF and AI parameters. Exercise induced an increase of plasma uric acid that was significantly higherboth in REM and CR. PELF 8-epi-PGF2α was significantly increased in CR and correlated with PF and AI parameters. These results suggest that oxidative stress occurring in heaves is correlated with PF and AI and may be locally assessed by PELFglutathione status, uric acid and 8-epi-PGF2α. Systemic repercussions are reflected by assay of GSH in resting horses and by uric acid in exercising horses.