Twenty-nine dogs undergoing a variety of surgical procedures were assigned randomly to one of two groups. All animals were premedicated with acepromazine (0–05 mg/kg) intramuscularly. Induction of anaesthesia was achieved with thiopentone sodium, or propofol in the case of sight hounds, and maintained with halothane in an oxygen/nitrous oxide mixture using a non-rebreathing circuit. Dogs in group 1 were given flunixin (1 mg/kg made up to 5 ml with 0–9 per cent saline) slowly intravenously 10 minutes before the halothane was switched off. Group 2 dogs received papaveretum (0–2 mg/kg made up to 5 ml with saline] administered as before. Using a visual analogue scale, the dogs were scored for sedation and for pain by trained theatre staff who were unaware of the analgesic used. Scoring was at15, 30, 60, 120, 240 and 360 minutes after analgesic administration. Seven dogs were withdrawn from the trial (three from the papaveretum group and four from the group which received flunixin) because analgesia was deemed unsatisfactory and these animals were given pethidine (3 mg/kg intramuscularly) which produced adequate analgesia within 15 minutes in all cases. Clinically, flunixin proved to be as effective a postoperative analgesic as papaveretum for up to six hours and was associated with less sedation, Pain scores were significantly different at two and four hours with flunixin providing more analgesia than papaveretum and at the four hour time point, flunixin was associated with significantly less sedation than papaveretum. From this study it was concluded that flunixin has a place in the treatment of acute post surgical pain, either alone or in combination with opioid analgesics where pain is refractory to treatment with clinical doses of opioids alone.