Fluid resuscitation is a basic treatment in hemorrhagic shock. We compared the circulatory responses to fluid resuscitation of 10% pentastarch with those of fresh whole blood and plasmanate in hemorrhagic shock. Eighteen mongrel dogs were bled 24 ml/kg and replaced by equivalent amounts of fresh whole blood(n=6, group B), pentastarch(n=6, group P) and plasmanate(n=6, group PL). Hemodynamic measurements and calculations were performed before and after bleeding and after volume therapy. The decrease of hematocrit and platelet count after volume replacement indicate that hemodilutional effect was maximum 30 min after volume therapy and significantly greater in group P than PL(p<0.05). Central venous pressure(CVP), pulmonary capillary wedge pressure(PCWP) and cardiac index(CI) were increased to 146-189%, 146-172% and 146-175% in group P, respectively during 60 min. These changes were significantly greater than group B and PL(p<0.05). There was delayed recovery of mean arterial pressure in group PL(92% 30 min after volume therapy) compared with group B and P(92% and 93% 5 min). Also group P and PL showed significant prolongation in prothrombin time and partial thromboplastin time during experiment(120 min) and these were significantly more prolonged in group P than PL(P<0.05). And group P showed similar O transport and O extraction ratio to those of group B. The increases in plasma catecholamine were observed after hemorrhage, but no significant changes 5 and 30 min after volume therapy. This suggests that the neurohumoral response to hemodilution was not marked. Mixed venous O2 saturation(SvO2) was directly proportional to CI during experiment(r=0.69, p<0.01), indicating that SvO2 can represent CI during shock and volume therapy. In conclusion, l0% pentastarch is useful as a substitute for fresh whole blood or plasmanate.