One hundred and thirty-eight nurses were asked to indicate the smallest meaningful reduction in pain from each of four hypothetical pain intensities: 100, 75, 50 and 25, on 100 mm visual analogue scales. The median values for the smallest meaningful reductions in pain were 31, 24, 18 and 10 mm, respectively, representing reductions in pain intensity of 31%, 32%, 36% and 40%, respectively. These tests were repeated in 110 patients before and after they had a lower third molar extraction under general anaesthesia. The patients' expectations of pain relief, pre- and postoperatively, were very similar to those observed in the nurses. For each of the four hypothetical pain intensities the median values for meaningful reductions in pain became greater following surgery. The pre-operative median reductions from the hypothetical pains 100, 75, 50 and 25 mm were 26, 20, 15 and 11 mm (26%, 27%, 29% and 44%), respectively. The corresponding postoperative reductions were 31, 24, 19 and 12 mm (31%, 32%, 38% and 48%). To achieve a meaningful reduction in pain postoperatively in 50% of patients it is necessary to reduce pain as represented by the visual analogue scale, by between 31 and 48%, depending on its initial intensity.