Catecholamines in plasma and tissue were determined during hemorrhagic shock in the rat. Two groups of rats were compared. 1. Awake rats bled to 70 mm Hg for 4 hours. 2. Anesthetized rats (pentobarbital sodium 60 mg/kg) bled to 35 mm Hg for 4 hours. The mortality rate was similar in both groups. The bled volume was also similar. The awake rats responded with tachycardia upon bleeding while the anesthetized rats responded with bradycardia. The basal plasma levels of noradrenaline (NA), adrenaline (A) and dopamine (DA) in the awake rats were 2.87, 4.09, and 0.51 nmol/l respectively and in the anesthetized rats 0.97, 0.54, and 0.56 nmol/l respectively. At the onset of bleeding there was a more rapid increase of plasma A and NA in the awake rats than in the anesthetized rats. In the awake rats plasma A reached its peak value (70 nmol/l) at 1 hour and then decreased, while NA showed a slow continuous rise to 17 nmol/l at 4 hours. In the anesthetized rats plasma A remained at a high level (about 60 nmol/l) between 1 and 4 hours, while there was a continuous rise of NA to 17 nmol/l at 4 hours. In these rats a very high DA level (17 nmol/l) was also found at 4 hours. The tissue content of NA was not significantly decreased in the heart while a significant decrease was seen in the skeletal muscle after bleeding for 4 hours. In the heart there was a substantial increase of A after bleeding. The A content of the adrenals decreased to about 25% of the initial value in the awake animals. The results show that barbiturate anesthesia considerably depresses the initial sympatho-adrenal response to bleeding.