The post-operative effects of laparotomy and common bile-duct ligation were investigated in rats. Bile-duct ligation caused a significant reduction in food and water consumption, body weight and locomotor activity in the immediate post-operative period. Animals which underwent laparotomy in which bile-duct ligation was not carried out (sham operated groups) had significantly less depression of food and water consumption and body weight than groups which underwent bile-duct ligation. The detrimental effects on food and water consumption and body weight could be significantly reduced by the administration of buprenorphine (0.05 mg/kg, s/c), but not by infiltration of the surgical wound with the long-acting local anaesthetic agent, bupivacaine. The reduction of the depressant effects of surgery on food and water consumption by the opioid analgesic buprenorphine suggests that some of these changes may be related to the presence of post-operative pain.