Ischemia-reperfusion (I/R) lung injury causes increased vascular permeability and edema. We developed an in vivo murine model of I/R allowing measurement of pulmonary vascular barrier function without airway occlusion. The left pulmonary artery (PA) was occluded with an exteriorized, slipknotted suture in anesthetized C57BL/6J mice. The effect of ischemic time was determined by subjecting mice to 5, 10, or 30 min of left lung ischemia followed by 150 min of reperfusion. The effect of reperfusion time was determined by subjecting mice to 30 min of left lung ischemia followed by 30 or 150 min of reperfusion. Changes in pulmonary vascular barrier function were measured with the Evans blue dye (EBD) technique, dual-isotope radiolabeled albumin (RA), bronchoalveolar lavage (BAL) protein concentration, and wet weight-to-dry weight ratio (WW/DW). Increasing left lung ischemia with constant reperfusion time or increasing left lung reperfusion time after constant ischemic time resulted in significant increases in left lung EBD content at all times compared with both right lung values and sham surgery mice. The effects of left lung ischemia on lung EBD were corroborated by RA but the effects of increasing reperfusion time differed, suggesting binding of EBD to lung tissue. An increase in WW/DW was only detected after 30 min of reperfusion, suggesting edema clearance. BAL protein concentrations were unaffected. We conclude that short periods of I/R, without airway occlusion, increase pulmonary vascular permeability in the in vivo mouse, providing a useful model to study molecular mechanisms of I/R lung injury.