In a randomized, double-blind, double-dummy, single-dose, parallel-group study, oral ibuprofen arginine(400 mg) was compared with intramuscular (i.m.)morphine sulphate (5 or 10 mg) for post-operative pain relief after orthopaedic surgery in 120 patients. The study medication was administered post-operatively at the time when each patient first requested pain relief for moderate to severe pain. Assessment of pain intensity and pain relief was made using standard visual analogue scales and verbal rating scores. In all three groups, there was a reduction in pain compared with baseline, measured by visual analogue scales and verbal rating scores, at all time points up to completion of the study at 240 min. For example, visual analogue scales decreased by 35 (10–52)mm at 1 h in the morphine 5 mg group, 24 (12–39)mm in morphine 10 mg group and 21 (8–38)mm in the ibuprofen arginine group (median and inter-quartile range). Verbal rating scores showed a similar pattern. Comparing the groups over the whole study period using the sum of pain intensity differences showed no significant differences in pain experience between the groups.Assessment of total pain relief also showed no significant differences. The incidence and types of side effect seen were similar in the three groups.