The free radicals play an important role in the pathogenesis of neoplastic transformation of the tissues. Superoxide dismutase is a metalloenzyme, protecting the cells from oxygen radical insult. The superoxide dismutase activity may therefore alter the cellular signaling pathways against the insults derived from oxidative stress especially in the tumor tissues. Therefore, it is considered that superoxide dismutase activity is crucial in affecting the survival of the cancer bearing patients. This study aims to investigate the level of superoxide dismutase activity in hepatocellular carcinoma tissues and correlate this with patients' survival after surgery for hepatocellular carcinoma. Thirty-six patients who had hepatectomy for hepatocellular carcinoma at the National Taiwan University Hospital from 1992 to 1993 were included in this study. Superoxide dismutase activity of the tumor tissues was determined. The results were correlated with the patients' survival. The patients were grouped based on their postoperative survival time. Those patients who were deceased less then one year after surgery were in group I. Group II included patients who survived more than one year but less than 3 years after operation. Group III patients survived more than 3 years but less than 5 years. Ten patients who survived longer than 5 years after surgical intervention were in group IV. Data were expressed as mean and analyzed with ANOVA. The demographic and clinical information of patients, such as age, gender, plasma albumin, globulin, alpha-fetoprotein levels, and hepatitis markers were comparable among these groups. The superoxide dismutase levels in the hepatocellular carcinoma were significantly higher in group IV than the other three groups (P < 0.05). Similarly, the superoxide dismutase levels of the hepatocellular carcinoma tissues from group III patients were significantly greater than those tissues from patients of either group I or group II. Tumor superoxide dismutase levels tended to be higher in group II than in group I, although it did not reach a statistical significance. Patients with higher superoxide dismutase levels in the hepatocellular carcinoma survived longer after hepatectomy. The superoxide dismutase levels of the tumor tissue may influence the malignancy and the outcome of the patients. It serves as prognostic factor for patients after hepatocellular carcinoma operation.