Glucagon was infused through the porta or through the left renal artery in dogs. Another group of dogs were infused with glomerulopressin through the left renal artery. It was observed that glucagon when infused through the portal vein enhanced the glomerulopressin production and the glomerular filtration rate (GFR). When glucagon was infused intrarenally it did not alter GRF but it had a direct tubular action decreasing sodium reabsorption in the proximal tubule. Glomerulopressin infused intrarenally increased GRF and potassium excretion. The results suggest that the increase in GFR was due to increase in glomerulopressin activity. There are three reasons for this statement: a) GRF increased when glomerulopressin activity was high, but not when there was a low activity, 5) intrarenally infused glomerulopressin produced a very significant change in the GFR of the infused kidney, while the GRF of the contralateral kidney remained unchanged and c) intrarenally administered glucagon had no effect on GFR.