1. The effect of renal lymphatic obstruction was studied by clearance methods with special reference to the renal response to the change in extra-cellular fluid (ECF) volume.
2. When the left renal lymphatics of anaesthetized dogs were obstructed, E/C (experimental over control kidney) ratios of urine volume (V) and sodium excretion (UNaV) increased significantly in spite of constancy of GFR E/C. This effect occurred during nondiuresis, water diuresis and during distal blockade (i.e. tubular inhibition by thiazide and ethacrynic acid).
3. As ECF was reduced by distal blockade, V and UNaV decreased rapidly in the control kidney, but only slightly in the experimental one, resulting in a sharp increase of V E/C and UNaV E/C.
4. The results indicate that intrarenal interstitial volume and/or pressure play an important role in sodium and water excretion and that it alters the renal response to a change in ECF volume.