The aim of our study was to measure the activity of plasma superoxide dismutase as an antioxidant enzyme in patients with exacerbation of bronchial asthma who needed hospital admission. Fourteen patients were studied (2 men - 12 women), mean age 58 ± 3.4 years. Upon admission and discharge forced expired volume of air in the first second (FEV1), partial oxygen pressure in arterial blood (PaO2) and activity of superoxide dismutase (SOD) using a colorimetric method, were measured. Additionally, severity criteria were recorded upon admission, such as the patient's inability to lie down, difficulty to speak, use of accessory respiratory muscles, wheezing, respiratory and heart rate and presence of pulsus paradoxus. Results showed a statistically significant reduction of SOD activity (46,6 ± 9 u/ml and 100 ± 15 u/ml respectively, p=0,0002) as a consequence of oxidative stress and a statistically significant correlation between SOD and FEV1 upon admission and between SOD upon admission and PaO2 upon discharge. However, no correlation was found between SOD activity, and severity criteria. Pneumon 2001, 14(3):232-237.