Fe(II) and Fe(III) are required for the catalysis of lipid peroxidation through generation of reactive oxygen species that damage cell membranes. This study investigated the effect of free radicals and lipid peroxidation, induced by intraperitoneal injection of iron-dextran in vivo, in the plasma of the sugar-induced hypertriglyceridemic and hypertensive male and female rats. Lipid peroxidation was measured by the malondialdehyde (MDA) equivalent, using a fluorescence method of 2-thiobarbituric acid reactive substances (TBARS). Iron increased TBARS generation by fourfold (P<.0001) in male control rats and by twofold (P<.01) in female control rats, and the difference between TBARS concentration in female as compared with male animals was statistically significant (P<.05). In the case of the sugar-fed group, iron-dextran produced an increase of TBARS concentration by twofold in both male (P<.001) and female rats (P<.01), and no significant difference in TBARS concentration was observed between sugar-fed female and male rats. The analysis of fatty acid composition by gas chromatography showed a significant diminution of 50% in the proportion of arachidonic acid (C20:4n-6) in the male control group in comparison with the female group (P<.0001). In female control rats, a small diminution in the proportion of C20:4n-6 and in the other polyunsaturated fatty acids was observed (P<.05). A significant difference in the C20:4n-6 proportion was found between the male and female group of control rats. In the sugar-fed group, iron induced a significant diminution of arachidonic acid (P<.001) in both female and male rats in comparison with the sugar-fed group without iron.