The effects of fluid resuscitation with 6% hetastarch, 5% albumin, or 0.9% saline solutions on plasma colloid osmotic pressure (COP) were examined in 26 patients with hypovolemic circulatory shock. One liter of hetastarch produced a 36% increase in COP compared to an 11% increase after 1 L of albumin (p < 0.001). One liter of saline resulted in a 12% decrease in COP (p < 0.05). The mean COP increased from 16.3 ± 1.6 (SE) mm Hg to a maximum of 23.7 ±1.4 mm Hg during the first 24 h of hetastarch resuscitation (p < 0.01), and from 17.0 ± 1.1 to 22.3 ± 1.5 mm Hg with albumin (p < 0.001). Saline resuscitation decreased the COP from 17.1 ± 1.1 mm Hg to a minimum of 12.7 ± 1.1 mm Hg (p < 0.02). These changes persisted from 2–5 days after resuscitation. Saline resuscitation required significantly larger amounts of fluid. The authors conclude that fluid resuscitation of circulatory shock with colloid solutions increases COP and requires less volume of resuscitative fluid.