The levels of high molecular weight (HMW) kininogen and pre-kallikrein in rat plasma were markedly reduced after single injection of bromelain (10 mg/kg, i.v.) and gradually recovered over a 72 hour period. The level of low molecular weight (LMW) kininogen, however, was not changed during this period. Rat pleurisy was induced by intrapleural injection of lambda-carrageenin. The levels of HMW kininogen and prekallikrein, but not of LMW kininogen, in the exudate were markedly decreased, when compared with those in plasma of the same animals. After pretreatment with disulfiram, oral administration of ethanol (2 g/kg) or intravenous injection of acetaldehyde (10 mg/kg) to rats caused significant decrease in the plasma level of LMW kininogen with no significant effect on the plasma HMW kininogen and prekallikrein levels. These results suggest that HMW and LMW kininogens may be consumed separately in vivo and play different roles.