IL6 and respiratory system disorder: Evaluation of these markers in foals with naturally occurring respiratory diseases is lacking.<h4>Objectives</h4>To determine if CRP and IL-6 were useful predictors of respiratory disease in foals from birth to weaning.<h4>Study design</h4>Prospective cohort study.<h4>Methods</h4>Periodic blood samples from 200 initially healthy foals were collected from birth to weaning on a farm with endemic Rhodococcus equi and Streptococcus equi pneumonia.