This report presents three studies of post-traumatic pulmonary insufficiency (PTPI). In the first no significant pulmonary hemodynamic or ventilatory changes in severely shocked baboons resuscitated with shed fresh blood or stored blood were observed over 48 or 84 hours. Second, a post-mortem study of patients receiving more than 5 units of blood within 24 hours of death showed some microemboli in the lungs in about two thirds. Patients with multiple microthrombi had received an average of 20.6 units of blood; patients with some or no microemboli 15.5 and 6.3, respectively. Third, in a review of the respiratory complications of 153 multiple-trauma patients, it was shown that the formerly severe problems with PTPI were now well managed clinically, that persistent respiratory failure was now occurring much later after injury, and occurred almost exclusively in patients with sepsis.Relation of the above data to previous reports in the literature led to the conclusion that the clinical significance of microaggregates in stored blood, if any, is low, and that ultrafiltration to remove microemboli only makes sense if it does not impede the rate of blood infusion and does not increase cost.