Marked gastric distention was-observed in rats 20 h after they underwent partial hepatectomy under isoflurane anesthesia and received buprenorphine (0.3 mg/kg of body weight) after surgery. Hardwood bedding comprised the bulk of the gastric contents. A study was undertaken to determine the cause of the pica behavior (consumption of non-nutritive substances) and resultant gastric distention. Ten-week-old male Sprague Dawley rats were randomly assigned to one of six groups. Group-1 rats (n = 11) underwent laparotomy under isoflurane anesthesia, with buprenorphine (0.3 mg/kg) administered after surgery. Group-2 rats (n = 12) underwent laparotomy under isoflurane anesthesia with buprenorphine (0.05 mg/kg) administered after surgery. Group-3 rats (n = 24) underwent laparotomy under isoflurane anesthesia, with saline administered after surgery. Isoflurane was administered at the same rate, concentration, and duration for all groups that underwent laparotomy (groups 1 to 3). Buprenorphine or saline was administered subcutaneously as a single injection when anesthesia was discontinued (groups 1 to 3). Group-4 rats (n = 6) received buprenorphine (0.3 mg/kg) only. Group-5 rats (n = 6) received buprenorphine (0.05 mg/kg) only. Group-6 rats (n = 12) received saline only. Rats not undergoing laparotomy (groups 4 to 6) received buprenorphine or saline 18 to 20 h before euthanasia. Rats were housed individually in filter-topped polycarbonate cages containing hardwood bedding. A purified, pelleted diet and water were offered ad libitum. Food and water consumption were measured over the posttreatment period. Eighteen to 20 h after treatment, rats were euthanized, each stomach and its contents were weighed, contents were examined grossly, and wet and dry gastric content weights were recorded. All weights were significantly (P < 0.05) increased in rats receiving buprenorphine administered after surgery (groups 1 and 2), compared with rats of the control group (group 3). Weights of the stomach and contents, wet gastric contents, and dry gastric contents were significantly (P < 0.05) increased in rats receiving 0.3 mg of buprenorphine/kg only (group 4), compared with values for their controls (group 6). Hardwood bedding comprised the bulk of the gastric contents in all groups receiving buprenorphine. Stomachs of rats not receiving buprenorphine contained the purified diet with little or no hardwood bedding. These results indicate that a single injection of buprenorphine at a dosage of 0.05 or 0.3 mg/kg resulted in rats ingesting hardwood bedding, leading to gastric distention. It was concluded that pica behavior associated with administration of buprenorphine should be considered when evaluating experimental data from rats housed on contact bedding.