Evaluation of the analgesic activity of indoprofen was carried out in patients with cancer pain under double-blind conditions and compared with aspirin and placebo. A randomized experimental design was followed. Single oral doses were given of the test drug (100 and 200 mg), aspirin (600 and 1,000 mg), and placebo. For measuring analgesia, 5-point pain intensity and pain relief semiquantitative scales were used. Potency ratio between drugs was calculated on SPID (sum of pain intensity differences) and TOTPAR (total pain relief) and resulted in 10.3 by combination of estimates. In a group of only 24 patients, the data supported the following conclusions: indoprofen at 100 and 200 mg single doses is effective in relieving cancer pain; it displays a dose-related analgesic effect comparable to that of aspirin with only one-tenth the dose.