AIM: To investigate the relationship between the superoxide dismutase (SOD), malondialdehyde (MDA) metabolic changes and the gastric carcinogenesis. METHODS: The SOD activity and MDA content were measured in the gastric tissues from the focus center, peripheral and far-end areas of gastric carcinoma (n = 52) and gastric ulcer (n=10). All the tissues were subjected to routine histological examinations and classifications. RESULTS: The SOD activity was greatly reduced but the MDA content was markedly increased in the center areas of the non-mucous gastric carcinoma (non-MGC); and the poorly differentiated gastric carcinoma varied. The SOD activity was gradually decreased and the MDA content was gradually increased in the tissues from the focus far-end, peripheral to center areas of non-MGC. Both of the SOD activity and the MDA content: were significantly declined and were respectively at same low level in the tissues from the focus center, peripheral, and far-end area with the mucous gastric carcinoma (MGC). In contrast to the gastric ulcer and grade I or II of non-MGC, the same level of the SOD activity and the MDA content were found in the focus center areas. Between non-MGC (groups A-D) and gastric ulcer (group F), the differences of SOD activity and MDA content were very noticeable in the gastric tissues from the focus peripheral and far-end areas, in which the SOD activity showed noticeable increase and the MDA content showed noticeable decrease in the gastric ulcer. CONCLUSION: The active free radical reaction in the gastric tissues can induce the carcinogenesis of non-MGC. The utmost low ability of antioxidation in the gastric tissues can induce the carcinogenesis of MGC. The metabolic change of the free radicals centralized mostly in the center of ulcerated lesions only, which suggested the ability of antioxidation was declined only in these lesions. However, the metabolism of free radicals varied significantly and the ability of antioxidation declined not only in the local focus area but also in the abroad gastric tissues with gastric carcinoma. METHODS: The SOD activity and MDA content were measured in the gastric tissues from the focus center, peripheral and far-end areas of the gastric activity (n = 52) and gastric ulcer (n = 10). All the tissues were subjected to routine histological examinations and classifications. RESULTS: The SOD activity was greatly reduced but the MDA content was markedly increased in the center areas of the The SOD activity was increasingly decreased in the tissues from the focus far-end, peripheral to center areas of non-MGC Both of the SOD activity and the MDA content: were significantly declined and were respectively at the same low level in the tissues from the focus center, peripheral, and far-end area with the mucous gas In contrast to the gastric ulcer and grade I or II of non-MGC, the same level of the SOD activity and the MDA content were found in the focus center areas. Between non-MGC (groups AD) and gastric ulcer (group F), the differences of SOD activity and MDA content were noticeable in the gastric tissues from the focus peripheral and far-end areas, in the the SOD activity showed noticeable increase and the MDA content showed noticeable decrease in the gastric The active free radical reaction in the gastric tissues can induce the carcinogenesis of non-MGC. The utmost low ability of antioxidation in the gastric tissues can induce the carcinogenesis of MGC. The metabolic change of the free radicals centralized mostly in the center of ulcerated lesions only, which suggested the ability of antioxidation was declined only in these lesions. However, the metabolism of free radicals varied significantly and the ability of antioxidation declined not only in the local focus area but also in the foreign gastric tissues with gastric carcinoma.