In two multicentric randomized, double-blind, parallel design trials the more appropriate dose of ketoprofen lysine salt suppositories, by considering benefit-risk ratio, was determined in children affected by acute inflammatory disease of respiratory or urinary tract with fever and pain. Fifty-three children ranging 6-36 months (infants) randomly assigned to 20, 30, 40 mg dose levels, and 54 children ranging 3-13 years (children) randomly assigned to 40, 60, 80 mg dose levels were included in the studies. Efficacy variables considered were hyperthermia and pain; body temperature was measured rectally, at fixed intervals and pain was evaluated by Maunuskela scale at the same interval times. Standard laboratory test were obtained at the beginning and end of treatment, and blood arterial pressure and heart rate were recorded regularly. Systemic and local tolerability were also determined. In infants all doses were associated with analgesia and temperature reduction; antipyretic effect was statistically significant starting from the first hour (p = 0.007). The dose of 30 mg resulted different from 20 mg dose from third hour (p < 0.05). The appropriate dose that better relate antipyretic and analgesic efficacy with a good tolerability was 30 mg. In children the analgesic and antipyretic efficacy was well established at all doses tested, however the effects were more marked and prolonged at 60 and 80 mg doses, with a better tolerability for 60 mg dose. The tolerability of all doses studied was good. Doses of 30 mg in infants and 60 mg in children correspond to a range of 2.0-3.5 mg of ketoprofen lysine salt for kg body weight, for each administration.