Renal lymph was collected from either capsular or hilar lymphatic vessels in anesthetized dogs. Collections were made during control periods and during two levels of elevated renal vein pressure. Increases in renal vein pressure resulted in increased lymph flow and decreases in capsular lymph protein, creatinine and PAH concentrations relative to those of concurrently collected arterial blood plasma. Although hilar lymph flow increased in response to elevated renal vein pressure, only the lymph creatinine concentration was decreased. It was concluded that peritubular capillary filtration may not be a major factor in determining renal lymph composition. In addition, it appears that the steady-state protein and PAH concentrations in the interstitial fluid of the outer cortex are more sensitive to solute washout during increased renal vein pressure than those of the inner cortex and outer medulla.