The hemodynamic relationship between renal venous pressure (RVP) and renal blood flow (RBF) during PEEP was investigated using adult mongrel dogs. When continuous mechanical ventilation (CMV) with 10 cm H2O of PEEP was applied to dogs previously on CMV with zero PEEP, RVP increased from 6.6 to 8.7 mm Hg (p less than .01), and left RBF decreased from 66 to 57 ml/min (p less than .05). RBF recovered by 49% of the difference as soon as PEEP was discontinued when the RVP elevation was maintained at the level observed during 10 cm H2O of PEEP. With 20 cm H2O of PEEP, RVP increased further to 10 mm Hg (p less than .01) and left RBF decreased to 48 ml/min (p less than .05). When the left renal vein was occluded and the RVP was maintained at the level seen during 20 cm H2O of PEEP, left RBF recovered only 50% of the difference from the flow during zero PEEP. We conclude that the reduction in RBF with PEEP application is caused by several factors; however, RVP elevation during CMV with PEEP is influential in decreasing RBF.