The efficacy and tolerability of acetylsalicylic acid, paracetamol, diclofenac, ibuprofen, indomethacin, pirprofen, sulindac, naproxen and suprofen were compared in the treatment of cancer pain. In a double-blind, within-patient randomized study, each drug was given for 1 week to eight patients and for another week to a further eight patients. A total of 65 patients were effectively treated; only 48 completed week 1 and 41 completed week 2. Naproxen, diclofenac and indomethacin were highly effective in pain relief (tested by means of a 100 mm visual analogue scale) and were relatively well tolerated. It is concluded that these non-steroidal anti-inflammatory drugs can be considered as first choice in the treatment of cancer pain.