1. [1-14C]Propachlor-GSH was perfused at 0.34, 3.4 and 34 mumol/h through the portal vein or the right renal artery of anaesthetized rats with biliary and ureteral cannulas. Urine was the predominant route for elimination of the 14C regardless of the route of perfusion. 2. Mercapturic acid conjugates were found to be the end-products of metabolism of the 14C-propachlor-GSH by rat kidneys and liver, indicating that all enzymes necessary for the catabolism of GSH conjugates to mercapturates were present in each of these tissues. 3. Perfusion of 14C-propachlor-GSH at 34 mumol/h appeared to exceed the metabolic capacity of both liver and kidneys for this substrate. At this dose, parent compound was detected in the bile of portally perfused rats, and the amounts of 14C recovered in bile, kidneys and carcasses of renally perfused rats were greater than when smaller dosages were perfused.