This study examined the role of delayed apoptosis of bronchial mucous cells as a contributing factor to mucus accumulation in equine recurrent airway obstruction (RAO). In pilot studies, Bcl-2, an apoptosis inhibitor, was detected in airway mucous cells of RAO-affected horses both in remission and during acute disease when most mucus was secreted. To study whether delayed apoptosis results in increased number of mucous cells during disease recovery, 6 RAO-affected and 6 control horses were fed hay for 5 days to induce inflammation and then pellets for 7 days to cause partial resolution of disease prior to euthanasia. RAO-affected horses had more airway obstruction and luminal mucus than control horses under both management systems. At the time of euthanasia, RAO-affected horses had more inflammation and Bcl-2-positive bronchial mucous cells than control animals. Horses with greater or less than 10 neutrophils per microliter of BALF had Bcl-2 staining in >50% or <10% of mucous cells, respectively. No differences in mucous cell number or the amount of stored mucosubstance was observed between RAO and control horses, but in RAO-affected animals, the amount of stored mucosubstance decreased as BALF neutrophil numbers increased. Because mucous cell numbers in both groups of horses were similar although mucous cells of only RAO-affected horses expressed Bcl-2 during recovery from acute disease, a conclusive role for Bcl-2 in prolonging bronchial mucous cell life could not be determined. Future studies need to compare horses that are kept in remission for prolonged periods when all mucous cells are fully developed.