We studied the effect of hemorrhagic shock, resuscitation, and recovery on the pulmonary microcirculation. We used lung lymph flow (QL) and lymph-to-plasma protein ratio as sensitive indices of transvascular fluid filtration rate and protein permeability. We measured pulmonary vascular pressures, cardiac output, blood gases, lymph flow, and lymph and plasma proteins before and during a 2-h period of shock, a 3-h period of resuscitation, and a 72-h period of recovery, in nine unanesthetized sheep with chronic lung lymph fistula. We found a 30% decrease in QL during early shock as animals were bled into bags containing an acetate citrate dextrose solution until aortic pressure was 50 Torr. QL gradually increased to or exceeded base line in five of nine animals during late shock as pulmonary vascula resistance increased by 250%. During the 3-h resuscitation period, mean QL increased by 110%, with the lymph-to-plasma protein ratio being significantly decreased, indicating no protein permeability change. In five of nine studies, lymph became visible bloody. The increased QL and lymph RBCs were felt to be secondary to an elevation in microvascular pressure. During the recovery period, pressures and QL returned to base line.