A multicentric, double-blind, randomized, parallel-group study was performed in patients with fever of diverse origin to test the tolerance and the antipyretic activity of single oral doses of 4-(p-fluorophenyl)-1-isopropyl-7-methyl-2(1H)-quinazolinone (fluproquazone) (200 mg, n = 18), acetylsalicylic acid (ASA) (1000 mg, n = 22) and placebo (n = 19). Whereas with placebo mean rectal temperature remained constant, a continuous fall was recorded with both active medications over the whole 3-h study period. With fluproquazone normalization of body temperature was nearly reached. Fluproquazone was more effective than placebo (p less than 0.001) and ASA (p less than 0.1), which in turn was more active than placebo (p less than 0.0001). No specific side-effects occurred.