In a single-blind random study, simultaneously carried out by five Pain Therapy and Palliative Care Centres, the analgesic power and side-effects of sodium naproxen (CAS 26159-34-2) and sodium diclofenac (CAS 15307-86-5) by mouth were compared in a group of 100 advanced cancer patients. The patients complained of somatic and/or visceral pain and were treated with non-steroid anti-inflammatories as required. The dose administered amounted to 550 mg every 12 h for sodium naproxen and to 100 mg every 12 h for sodium diclofenac. The study stressed the similar analgesic effect of the two drugs--pain intensity and duration decreased by half in the first week of treatment--and a comparatively low morbidity rate.