Antipyretic effect and tolerability of alpha-methyl-4-(2-thienylcarbonyl)-phenyl acetic acid (suprofen, Suprol), syrup and paracetamol (acetaminophen) were compared within the scope of the present randomized single-blind study; the test population included a total of 115 children ranging in age from 6 months to 12 years. All patients were admitted to the hospital with an average temperature of 39.3 degrees C, their disease being caused by bacterial or viral infections. The dose levels for treatment with syrup depended upon the children's age and body weight. Treatment was in most cases given for two days; a three-times-a-day schedule was used. The (rectal) temperature as well as pulse and respiratory rates were measured prior to treatment and 0.5, 1, 1.5, 2, 3, 4, 5, 6 h after first administration of the test preparations. The results showed that the antipyretic effect of suprofen was in both age groups at all rating times statistically significantly superior to that of paracetamol. Pulse and respiratory rates dropped in both age groups after treatment; the means were within the normal range at all rating times. Adverse drug reactions were seen in 5 patients on suprofen and in 3 cases on paracetamol. It is, however, questionable whether such reactions are drug-dependent.