The relationship between the levels of total sialic acid (TSA), lipid peroxide (LPO), ascorbate and superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities in Fusarium acuminatum and Fusarium equiseti was investigated depending on the urea concentration. SOD, CAT and GSH-Px activities of E acuminatum have been increased up to 15 g/L urea, but increases of urea concentration to 25 g/L caused to decreases in the enzyme activity. In addition, SOD and CAT activities of F. equiseti have been negatively correlated depending on the increase in urea concentration during incubation period. However, there was no significant difference in SOD activity of F. equiseti grown 5-15 g/L urea supplemented medium. The lowest values of GSH-Px activities of both Fusarium species were determined at 25 g/L urea. As another antioxidant enzyme, ascorbate production of F. acuminatum and F. equiseti were negatively correlated with urea concentration used. At the same time, the variations of sialic acid of the Fusarium species showed positive correlation with antioxidant and it was negatively correlated with membrane LPO levels. The results suggest that antioxidant enzymes are effective parameter on the membrane bound sialic acid and lipid peroxidation level, which have an important impact on life span. (c) 2005 Elsevier Inc. All rights reserved.