Hypertension is an important cause of cardiovascular morbidity and mortality and is age dependent. Moreover, the rate of aging and the onset of age-related diseases are modulated by the stress response. The aim was investigate the renal and oxidative response to chronic stress in aged rats, as predisposing factors to increase blood pressure with age. Male Wistar rats of three (young) or eight (old) months of age were divided into: controls or chronic immobilized rats. Blood pressure, natremia, aldosterone, corticosterone, gamma-glutamyl-transferase, nitrites, urine sodium and renal malonyldialdehyde, catalase and superoxide dismutase activitywere measured. Corticosterone and blood pressure were higher in old than young stressed rats.Antinatriuresis in all stressed rats was found. Natremia increased only in old stressed rats. No differences were found in superoxide dismutase and catalase activity in response to stress but a major increase in gamma-glutamyl-transferase and renalmalonyldialdehyde and a decrease in nitrites were observed in old stressed rats. Aged rats have an increased oxidative state and a greater stress response. Increased natremia, bigger oxidative stress and reducedNObioavailability in stressed old than young rats could cause an attenuated vasorelaxant response and could explain, in part, the blood pressure increase with age.