Oxidative stress often plays a central role in the development of endothelial dysfunction caused by cardiovascular risk factors. Our aim was to examine the effects of acute exercise on the glutathione antioxidant system in lean and obese hypertension. Nineteen obese hypertensive (OH) and 13 lean hypertensive (HYP) adolescents performed a single bout of exercise on a cycle ergometer. Before and after the exercise, oxidized and reduced glutathione (GSSG, GSH) were determined in blood samples together with those of 18 controls. Acetylphenylhidrazine (APH)-test was used to assess the capacity of glutathione regeneration in erythrocytes. We found significantly higher basal GSSG levels in both patient groups and GSSG/GSH ratio in HYP patients, as compared with the controls (p<0,05). The non-significant basal difference between patient groups reached the level of significance after exercise (p<0,05). Following the APH-test, residual GSH ratio was significantly lower in obese hypertensives than in HYP patients (p<0,05). Moderate exercise exerts distinct effects on the glutathione system in obese and lean hypertension, suggesting that their pathomechanisms might be different.