To determine the effects of infusion of large volumes of crystalloid, a series of dogs was subjected to intravenous injection of oleic acid and moderate hypovolemic shock for 1 hour. They were then resuscitated with 50 cc/kg of Ringer's lactate in 30 minutes followed by blood replacement, and another 50 cc/kg of Ringer's lactate over 1 hour in one group and 2 hours in the other. Eight of nine receiving the fast infusion died during the first 2 days, and seven of eight receiving the slow infusion lived for the full 3 days of the study. The dogs that died all had large intrapulmonary shunts and gross pulmonary edema at autopsy. Both groups received the same total amount of fluid. No differences in vascular pressure or cardiac function large enough to explain the differences were found. The critical difference was the rate of fluid infusion. The high-permeability pulmonary edema appears to have been aggravated by a transitent pulmonary overperfusion induced by fast infusion of fluid.