Shunting of radionuclide labeled 9 micron diameter microspheres by the systemic circulation, and 6 body regions was measured in two dog shock models: endotoxic shock (1 mg/kg E. Coli endotoxin intravenously) and sepsis and septic shock (5 days after cecal ligation). Mean systemic arterial blood pressure was significantly lower than control in both the endotoxic and septic shock groups. Mean systemic shunting was 7.7% in the control group and 7.3% and 4.3% respectively in the endotoxic and septic shock groups. Regional shunting of the head, heart, and skeletal muscle were not significantly different in the three groups. However, mean shunting in the splanchnic circulation was 36.5% in the septic shock group as compared to 18.6% in the control group (p less than 0.05). Mean kidney shunting in the endotoxic group was 15.1% compared to 4% in the control group (p less than 0.05). During resuscitation with crystalloid, mannitol, blood, and cortiocosteroids mean aterial blood pressure and cardiac index increased but systemic arterial-venous shunting was 3.8 and 4.3% in endotoxic and septic shock respectively. These data show that systemic anatomic arterial-venous shunting is small and not different from control in both dog shock models, and regional arterial-venous shunting is increased only in the splanchnic circulation in the septic model and in the kidney in the endotoxin model.