BACKGROUND: Oxidant-antioxidant imbalance may play an important role in the development and progression of bronchial asthma. However, the role of blood antioxidants especially in asthma exacerbation has not been fully discussed.OBJECTIVE: This study examines a part of the intracellular antioxidant defense mechanism in asthmatic patients admitted to hospital due to severe exacerbation of their disease.METHODS: Peripheral blood Erythrocyte Superoxide Dismutase (SOD) activity was measured in 38 patients (33 men - 5 women, with a mean age of 56 +/- 2.8 yrs), using a colorimetric method. On the days of admission and discharge the Forced Expiratory Volume in 1 second (FEV1) and the Partial arterial Oxygen pressure (PaO2) were recorded and correlated with SOD activity at the same time.RESULTS: A statistically significant decrease of SOD activity was observed on the day of admission compared to SOD activity on the day of discharge (43.64 +/- 31.78 vs. 96.16 +/- 54.05 units/ml, p < 0.001), suggesting the presence of oxidative stress during an asthma attack. A statistically significant correlation was observed between FEV1 on admission and SOD activity at the same time (r = 0.57, p < 0.001). Furthermore, SOD activity on admission was correlated with PaO2 on discharge (r = 0.55, p < 0.001), as well as SOD on discharge with PaO2 on discharge (r = 0.53, p = 0.001).CONCLUSIONS: Decreased systemic erythrocyte SOD activity was observed during asthma attacks. This activity was correlated with severity criteria such as FEV1 and PaO2. Therefore, it seems that measurement of SOD activity could be a useful tool in the evaluation of an asthma attack. The supplementary administration of antioxidants in the future needs further clarification.