The clinical course of rhinovirus-associated wheezing illnesses is difficult to predict. We measured lactate dehydrogenase (LDH) concentrations, rhinovirus load, antiviral and proinflammatory cytokines in nasal washes obtained from 126 preschool children with RV wheezy bronchitis. LDH values were inversely associated with subsequent need for oxygen therapy. LDH may be a useful biomarker predicting disease severity in rhinovirus wheezy bronchitis.