Plasma endothelin 1 (ET1) was determined by radioimmunoassay in 28 cases of acute attack of asthma (attack group), 23 subjects of non-symptomatic asthma (remission group) and 20 normal volunteers (control group). The results showed that the plasma ET1 in attack group (13.4 +/- 5.2 fmol/ml) was much higher than that in both remission group (8.4 +/- 3.9 fmol/ml, P < 0.01) and control group (6.6 +/- 2.6 fmol/ml, P < 0.01). However, there was no significant difference between remission group and control group. The plasma ET1 level revealed notably negative correlation to PaO2 and FEV1% (r = -0.8257, r = -0.8157, P < 0.01). The results suggested that ET1 probably involved in pathophysiologic process of acute attack of bronchial asthma.