The effect of renal denervation on the increase in plasma renin levels during continuous positive-pressure ventilation (CPPV) was studied in anesthetized dogs. Renin secretion was measured in a group of dogs with intact renal nerves and a group which had previously undergone bilateral renal denervation. Renal perfusion pressure was maintained constant throughout the experiment. Renin secretion increased significantly during application of CPPV with a positive and expiratory pressure of 10 cm water in the dogs of the intact group but was not altered in dogs of the denervated group. These results support the conclusion that CPPV increases renin secretion by reflexly altering renal nerve activity.