Sixty-two patients requiring regular treatment for osteoarthritis were entered into a 6-month open assessment of 1.5 g naproxen daily. Fourteen patients withdrew from the study because of side-effects, 9 because of poor efficacy and 2 for a combination of these reasons. Most side-effects related to the gastro-intestinal tract and were not of a serious nature, although 1 patient had a gastro-intestinal bleed at 24 weeks. A further patient developed neutropenia, but its relationship to naproxen therapy was considered unknown. Short-term studies of 1.5 g naproxen daily have shown an increased efficacy compared to lower doses with no increase in side-effects. It is concluded that the results of this study increase the confidence with which such a dose can be used.