The “inflammatory airway disease” (IAD) is a very common syndrome in young racehorse in training. Clinical signs are subtle including decreased performance, mild exercise intolerance and chronic cough. The purpose of the present study is to determine the incidence of 1) mucus accumulation, 2) tracheal neutrophylia and 3) tracheal infection with streptococci among poor performing, chronically coughing Standardbred horses. Streptococcus equi subsp zooepidemicus and Streptococcus pneumoniae was not always associated with mucus or high neutrophils percentage but the higher number of bacteria was found in horses with the higher mucus score. Nevertheless, the role of streptococci in IAD of Strandardbred horses and involvement of other etiological agents needs further investigations.