The inflammatory airway injury in Cystic Fibrosis can be lessened by oral ibuprofen therapy provided airway injury is in its early stages. The most important time to offer this therapy is, therefore, before or during the early phases of airway inflammation and injury in young children with CF who cannot take tablets of ibuprofen; liquid formulations are needed to treat them. The pharmacokinetics of liquid ibuprofen is not known in children with CF<6 years of age, and it may differ in infants, toddlers and preschool children from older children and adults with CF. The absorption of liquid ibuprofen may also differ from tablet formulations of ibuprofen. This study will describe the pharmacokinetics of liquid ibuprofen in infants, toddlers and preschool children. It is anticipated that liquid ibuprofen is absorbed faster, more uniformly and more completely than tablet formulation. As a result, plasma concentrations will rise faster, reach a peak sooner and then decay in a more predictable fashion.