Following hepatectomy, arterial concentrations of thromboxane B2(TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), which are stable metabolites of thromboxane A2(TXA2) and prostaglandin I2(PGI2), were measured by radioimmunoassay in 17 cirrhotic and 9 non-cirrhotic patients to assess the role of TXB2 and PGI2 in patients with liver dysfunction during hepatectomy. In both cirrhotic and non-cirrhotic patients, arterial TXB2 and 6-keto-PGF1 alpha levels significantly increased during hepatectomy and decreased to preoperative levels at the 1st postoperative day (1-POD). The TXB2/6-keto-PGF1 alpha ratio significantly decreased during hepatectomy and at 1-POD. There were no significant differences in changes of TXB2 and PGI2 levels between cirrhotic and non-cirrhotic patients. In cirrhotic patients with poor hepatic reserve, whose ICG K values were less than 0.08, arterial 6-keto-PGF1 alpha levels were significantly higher and the ratio were significantly lower than in cirrhotic patients with good hepatic reserve and non-cirrhotic patients before and after operation. Based on these results, it is concluded that the TXA2/PGI2 ratio becomes low after hepatectomy and the ratio is lower in cirrhotic patients with poor hepatic reserve.