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Exercise increases the generation of oxygen free radicals and lipid peroxidation. The aim of this study was to investigate the oxidant and antioxidant status in sedentary middle-aged (36.8 ± 5.4 years, n=20) and postmenopausal women (51.4 ± 3.3 years, n=11) before and after acute calisthenic exercise. Both subject groups performed an acute calisthenic exercise for 55 minutes. The intensity of the exercise was 60–70% of maximal heart rate, as determined by Karvonen et al. Plasma malondialdehyde (MDA), gluathione (GSH), ascorbic acid (AA) and nitric oxide (NOx) levels were determined spectrophotometrically. The postmenopausal group's pre-exercise MDA levels were high and GSH levels were low, compared with those of the middle aged group. This result indicated increased lipid peroxidation after menopause. In both groups, plasma MDA levels and NOx levels increased and plasma AA levels decreased following calisthenic exercise. The present study indicates for the first time that plasma MDA levels increase significantly after a bout of acute calisthenic exercise, involving all large muscle groups at 60–70% of maximal heart rate while plasma AA levels decrease concurrently. These effects may be due to increased lipid peroxidation in both middle aged and postmenopausal women. The finding of low plasma GSH levels and high plasma MDA levels in the postmenopausal group suggests the possible development of a disturbance in the oxidant and antioxidant status after menopause. Reduced levels of AA following acute calisthenic exercise might indicate the consumption of plasma antioxidants protecting the plasma lipids against the damage of lipid peroxidation. [ABSTRACT FROM AUTHOR]