Ibuprofen may be an alternative to acetaminophen to control fever in children but little is known about its pharmacokinetics in pediatric patients. We studied 17 patients (age 3-10 yr) with fever; the most prevalent diagnoses were streptococcal pharyngitis and otitis media. Ibuprofen liquid was given as a single dose, 5 mg/kg (9 patients) or 10 mg/kg (8 patients). Multiple blood samples were collected over 8 hours and analyzed by HPLC. The maximum observed serum concentrations of ibuprofen ranged from 17-42 micrograms.ml-1 at 5 mg.kg-1 and 25-53 micrograms.ml-1 at 10 mg.kg-1 doses. Pharmacokinetics did not appear to be affected by ibuprofen dose. Mean tmax, oral clearance and elimination half life were 1.1 h, 1.2 ml.min-1.kg-1, and 1.6 h, respectively in patients at 5 mg.kg-1 doses; the corresponding values were 1.2 h, 1.4 ml.min-1.kg-1, and 1.6 h in those receiving 10 mg.kg-1 doses. There was no relationship between age and ibuprofen kinetics. No adverse effects occurred in any patients. These data suggest that ibuprofen pharmacokinetics may not be affected by dose between 5 and 10 mg/kg or age between 3 and 10 years.