The aim of this work was to study the temporare variation of oxidative stress in the plasma and erythrocytes (CR) of renal transplant patients We determined total glutathione (GST), as well as oxidized (GSSG) and reduced (GSH) fractions and the activity of glutathione peroxidase (G-px), glutathione reductase (G-red) and glutathione transferase (GSt). Determinations were performed 48 hours before transplant as well as 1 and 2 weeks after the renal transplant. The results showed a high "oxidative stress" rate, resulting from the equilibrium between the production of free radicals and the activity of antioxidants, the former being higher proportionally. Immediately after the transplant, there was an increase in oxidative stress, which resulted in an increased G-red, a marked decrease in plasma and in erythrocyte G-px (CR9 and an abrupt drop both in GST levels in plasma and in GSG (as well as in the [GSH]/[GSSG] relationship). Thereafter there was a significant improvement in the activity of antioxidant enzymes, but without normalization; the total glutathione levels and the activity of various enzymes approached the average values of the control group.