The pharmacokinetics of racemic ibuprofen and its stereoisomers have been described in adults, but little has been reported for children. The pharmacodynamics of acetaminophen and ibuprofen have not been well described in either adults or children. Children (N = 39; age range, 11 months to 11 1/2 years) were randomly selected to receive a single dose of either 6 mg/kg of liquid ibuprofen or 10 to 15 mg/kg of liquid acetaminophen (mean +/- dose given, 11.6 +/- 0.7). Pharmacokinetic and pharmacodynamic analyses were performed with temperature as the effect parameter and mean acetaminophen, total ibuprofen, and ibuprofen stereoisomer concentrations over time. Time of maximum serum concentrations for ibuprofen was 54.05 minutes versus 27.0 minutes for acetaminophen, time to maximum temperature decrease was 183 minutes for ibuprofen and 133 minutes for acetaminophen. Temperature reduction for the ibuprofen dose was significantly different than that of the acetaminophen dose at later time points (240, 300, 360, 420, and 480 minutes). Further pharmacokinetic-pharmacodynamic studies with use of individual ibuprofen stereoisomers and other dosing regimens are indicated.