In children, tiaprofenic acid (TA), a non steroidal antiinflammatory drug, propionic-acid derivative, has been proven effective in the treatment of symptoms of tonsillitis and pharyngitis but not yet in the symptomatic treatment of fever. This double-blind, parallel group, placebo (Pl) controlled study was designed in order to demonstrate the antipyretic activity of TA. The co-prescription of other antipyretic medications in children may therefore be avoided. Two groups of children, 29 (TA group) and 26 (Pl group), were included and received either 4.2 +/- 0.5 mg/kg of TA given orally in a single dose or a Pl match. Rectal temperature was recorded just before and 1, 2, 4 and 6 hours after dosing. The maximum temperature decrease was significantly greater in the TA group (-1.3 degrees C +/- 0.7 degree C) than in the Pl group (-0.4 degree C +/- 0.8 degree C). The percentage of children who needed a rescue treatment during the study was 35% (10/29) and 62% (16/26) in the TA and Pl group, respectively. The rescue treatment was composed of a single oral acetaminophen dose in case of fever above 39.5 degrees C or if the temperature decrease was not at least equal to 0.6 degree C four hours after dosing. No major side effect was reported by the parents during the study period. In conclusion, TA at a single mean 4.2 mg/kg oral dose, is an effective antipyretic drug in febrile children. The duration of the antipyretic effect was estimated as at least four hours.