The enhancing effect on liver metastasis produced by the excessive surgical stress of thoraco-laparotomy (TL), and its regulation with a radical scavenger, were studied in 10-week-old Donryu rats. The rats were divided into three groups: those given thoraco-laparotomy for 1 h (the TL group); those given laparotomy alone for 1 h (the L group); those given a short laparotomy (the C group). The effects of treatment with 5 mg/kg of EPC-K1 was assessed in the TL group. A rat hepatocellular carcinoma cell line AH 60C (5 x 10(5) cells) was administered into the portal vein under general anesthesia. The number of metastatic liver nodules was counted 3 weeks later, and the lipid peroxide (LPO) levels of the liver and serum were measured by the TBA method on postoperative days (PODs) 1, 2, and 3. The number of metastatic liver nodules was 40.6 +/- 29.7, 15.0 +/- 15.8, and 13.7 +/- 9.4 in the TL, L, and C groups, respectively. When EPC-K1 was administered to the TL group, the LPO level on POD 1 decreased from 49.8 +/- 25.8 to 18.9 +/- 7.9 nM/g, and the number of metastatic liver nodules decreased from 27.2 +/- 30.0 to 8.9 +/- 12.7 in parallel. The findings of this study suggested that the excessive surgical stress produced by thoraco-laparotomy enhanced liver metastasis in parallel with an increase in LPO levels; however, the radical scavenger EPC-K1 could aid in reversing this effect.