The blood levels of epinephrine and its metabolites which were obtained when the drug was given by both the intravenous (IV) and endotracheal (ET) routes were compared. Anesthetized dogs were subjected to radioactive epinephrine in doses of 0.005, 0.03, 0.06, and 0.09 mg/kg administered both intravenously and endotracheally. Blood levels were obtained at 0.25, 0.75, 1.5, 3, 5, 10 and 30 minutes following injection and analyzed by thin layer chromatography. The maximum measured concentration following IV injection was observed at 15 seconds. Epinephrine was rapidly metabolized with 20% of the original concentration detected at 5 minutes following IV injection. When the drug was given by the ET route, the maximum measured concentration was similarly observed at 15 seconds. Following ET installation, initial blood concentrations are sustained over a much longer period of time and 80% of the initial concentration was detected at 5 minutes. Maximum concentrations are approximately one-tenth of those achieved with an equal IV dosage. It is concluded that endotracheally and intravenously administered epinephrine rapidly reach maximum blood levels although there are differences in kinetics between the two routes.