1 The aim of the present study was to investigate the contribution of bradykinin (BK) B 1 and B 2 receptors in a model of type III hypersensitivity, the reverse passive Arthus reaction (RPA), in wildtype mice and transgenic B 2 knockout littermates. 2 BK (10 mg mouse 71 ) or bovine serum albumin (0.5 mg mouse 71 ) induced a sustained Evans blue extravasation for more than 80 min in naive or rabbit anti-bovine serum albumin-treated mice (RPA model), respectively. The response to the two stimuli was prevented by the B 2 receptor antagonist, HOE-140, but not by [Leu 8 ]desArg 9 -BK (B 1 receptor antagonist). 3 In contrast to the wild-type littermates, RPA and bradykinin were unable to trigger an increase in plasma extravasation in B 2 knockout mice. 4 Furthermore, endothelin-1 (5 mg mouse 71 ) and a selective NK-1 receptor agonist [Sar 9 ,Met (O 2 ) 11 ]-SP (20 mg mouse 71 ), triggered a signi®cant increase in peritoneal plasma extravasation in both wild-type and B 2 knockout animals. 5 A pretreatment with indomethacin (200 mg mouse 71 ) signi®cantly reduced the RPA-induced but not the BK-induced increase in Evans blue extravasation. Furthermore, RPA, but not BK, triggered a signi®cant indomethacin-sensitive increase in peritoneal prostaglandin E 2 content. 6 Our results suggest a pivotal role for B 2 receptors in the mechanism of plasma extravasation which occurs during the reverse passive Arthus reaction in the mouse. Moreover, our results suggest an important contribution of prostanoids in the plasma leakage mechanisms triggered by RPA but not by bradykinin.