The changes in cardiac output (Q), regional blood blow (Qr) and regional vascular resistance, and arterial pressure were studied in rats subjected to moderate (LD0) or severe (LD50) traumatic shock. Q and Qr were determined using microspheres at 15, 60 and 180 min posttrauma. Arterial pressure decreased in both groups at 15 min and recovered by 3 hr after sublethal (LD0) trauma, while arterial pressure did not return to control levels after LD50 trauma. Q decreased in both groups at 15 min and returned to control only in the LD0 trauma group by 3 hr. Cerebral, coronary, and hepatic arterial flows and resistances were maintained in both groups. Renal, intestinal, and splenic flows decreased and resistances increased in both groups by 15 min and returned to control levels by 3 hr only in the LD0 trauma group. Total hepatic and hepatic portal flows decreased at 60 min and returned to control levels at 3 hr after LD0 trauma, while there was significant depression in these parameters 3 hr after LD50 trauma. Therefore, sublethal and severe trauma resulted in early redistribution of flow favoring the coronary, cerebral, and hepatic arterial beds. However, renal, intestinal, splenic, and portal flows remained depressed only in severely traumatized rats, suggesting that continued hypoperfusion is a factor in the multiple organ failure and death following severe traumatic injury.