Recently, endothelin-1 (ET-1) has a potent of contractive effect to bronchial smooth muscle, and it suggests that ET-1 contributes to pathophysiology of bronchial asthma. To study the role of endothelin-1 (ET-1) in allergic asthma, we measured ET concentration in plasma and in sputum of nine allergic subjects following allergen provocation by using sandwich-enzyme immunoassay (EIA). ET-1 concentration in plasma were higher during IAR (2.31 +/- 0.24 pg/ml) (0.05 < p < 0.1) and LAR (2.55 +/- 0.27 pg/ml) (0.05 < p < 0.1) than prechallenge value (1.99 +/- 0.23 pg/ml) but there was no significant difference. On the other hand ET-1 concentration in sputum were significantly higher during IAR (14.75 +/- 2.77 pg/ml) (p < 0.05) and LAR (18.51 +/- 4.57 pg/ml) (p < 0.05) than prechallenge values (4.29 +/- 2.55 pg/ml). Thus these results suggest that ET-1 play a role of allergic bronchoconstraction (IAR and LAR) after allergen challenge.