This study evaluated the effects of varying colloid concentrations and infusion volumes on survival and plasma volume expansion in rats subjected to an intestinal ischemic shock. Up to 10% solutions of albumin and dextran-40 in lactated Ringer's solution, infused over a 6-h period, had the same effects on hematocrit (Hct) changes and survival patterns. Mean Hct values (45% to 50%) were independent of colloid solution concentration. With lactated Ringer's solution alone, Hct was 55%, despite the very large volume used; and less than 3% of the infused lactated Ringer's solution remained as plasma volume at 3 and 6 h of infusion. With increasing colloid concentration a greater proportion of the infused volume contributed to plasma volume. Of a 10% colloid solution, 50% and 34% remained as plasma volume at 3 and 6 h. For colloid concentrations between 1% and 3%, there was an equal distribution of infused fluid between the extracellular fluid space and the plasma. Survival rate, as measured by blood volume expansion, was greater with colloid solution concentrations between 2% and 4%.