The aim of the present study was to investigate the antipyretic effect of alpha-methyl-4-(2-thienylcarbonyl)-phenyl acetic acid (suprofen, Suprol) 300 mg suppositories compared to placebo in patients with fever of various etiology. The trial was designed as a randomized double-blind study including 30 patients per treatment group. After insertion of the suppository, temperatures were measured after 30 min, 1, 2, 3, 31/2, 4, 5, and 6 h. The study was performed at four investigational centers. At the end of the study, a total of 61 patients could be evaluated: 27 on suprofen, 34 on placebo. There were no statistically significant differences in the anamnestic data. The mean age of the subjects on suprofen was 66.5 years, and on placebo 61.3 years. Prior to treatment, the mean temperatures in the two treatment groups were 38.8 and 38.9 degrees C, respectively. In the suprofen group, the temperature dropped to a mean of 37.9 degrees C within 3 h and to 37.6 degrees C within 6 h. The decrease in temperature was less marked in the placebo group; here the mean temperature was 38.4 degrees C after 3 h and 38.2 degrees C after 6 h. Suprofen was found to be superior to placebo throughout the study, the differences being statistically significant after 3 h up to 6 h. The only side effect experienced by a subject on suprofen was vomiting.