The effects of stem bromelain on the plasma kallikrein system, bradykinin levels and plasma exudation at the inflammatory site were examined in rats with a kaolin-induced inflammation of an air pouch. Bromelain (5, 7.5 mg/kg) caused a dose-dependent decrease of bradykinin levels at the inflammatory site and a parallel decrease of the prekallikrein levels in sera. Plasma exudation was also reduced dose dependently. Bradykinin-degrading activity in sera was elevated after treatment with bromelain, although it was unchanged in the pouch fluid. These data indicate that bromelain inhibits plasma exudation through inhibiting the generation of bradykinin at the inflammatory site via depletion of the plasma kallikrein system.