Rat urinary kallikrein (RUK) injected intravenously to the rat rapidly disappeared from the blood circulation and mainly distributed to the liver. RUK was also incorporated to the primary cultured rat hepatocytes. The amounts of RUK incorporated into the hepatocytes increased by preincubation of RUK with rat plasma. These results and SDS-PAGE analysis suggested some plasma components may be involved in tissue kallikrein clearance in the blood.