Intrarenal arterial infusions of sodium and potassium salts with anions other than chloride were given to evaluate the role of the chloride ion in influencing renin secretion (RS). The studies were conducted in dogs with thoracic caval constriction. Sodium lactate increased renal venous plasma sodium concentration (RVPNa) from 142 to 166 meq/liter (n, 6); RS decreased from 3,070 to 1,510 ng angiotensin/min (P less than 0.005). Arterial blood pressure and renal blood flow were not changed appreciably. Sodium excretion (ENa) increased, whereas chloride excretion (EC1) fell during the first three 15-min infusion periods. Potassium lactate increased renal venous plasma potassium concentration from 4.1 to 6.2 meq/liter (N, b). RS decreased during the first three 15-min periods of infusion (from 3,470 to 2,180 ng angiotensin/min, P less than 0.01). ENa and EC1 increased during the infusion. Potassium sulfate also decreased RS, and EC1 was usually increased. The results with sodium lactate favor a role for sodium compared with chloride in mediating the decreased renin release, but there are other possible interpretations which have been discussed. Additional studies are needed to resolve the role of chloride during potassium infusion.