Prevention of unnecessary pain in laboratory animals requires reliable and practically useful tools for assessing pain severity and analgesic efficacy. We have used a behaviour-based pain scoring system to determine the duration of pain resulting from laparotomy, and the duration of analgesia afforded by orally administered (p.o.) buprenorphine and subcutaneously administered (s.c.) carprofen or buprenorphine in rats. One hour before laparotomy Fisher 344 rats received either saline as a control (0.2 ml/100 g s.c.), carprofen (5 mg/kg s.c.) or buprenorphine (0.05 mg/kg s.c. or 0.4 mg/kg p.o.). The rats were housed singly for 10-min periods of behaviour recording, beginning 30 min after completing surgery. Recording was repeated at three time points every 2 h. The behaviour of controls was distinct from that of the analgesic-treated animals throughout recording; however, the major signs of pain (back-arching, staggering and writhing) were prominent during only the first 270 min in the saline group. This was followed by a period of more subtle differences between the saline- and drug-treated groups. It was concluded that the most acutely painful effects of surgery in this model lasted for between 270 and 390 min, and that this was alleviated throughout its duration by subcutaneously administered carprofen or buprenorphine, and also buprenorphine administered orally. The study demonstrates a clinically relevant and practically useful approach to assessing the duration of post-surgical abdominal pain and analgesic effects in rats.