In a clinical double-blind study, the analgesic efficacy and the side-effects of nimesulide (Aulin, CAS 51803-78-2) and naproxen administered to 68 patients affected by advanced cancer pain were compared. Patients were treated with non-steroidal anti-inflammatory drugs according to the first step of the pharmacological analgesic scale of the WHO. The dose administered was 200 mg b.i.d. (every 12 h) for nimesulide and 500 mg b.i.d. (every 12 h) for naproxen. From this study the analgesic effect and the tolerability of the two drugs appeared to be similar. Both drugs resulted to be effective with a low incidence of adverse events that may be related to their use.