We have previously reported that infusion of CaCl2 into the renal artery of the dog inhibits renin release. To evaluate the possible importance of the anion delivered with calcium, similar experiments were performed in 10 dogs with equivalent amounts of calcium gluconate (0.3 mg. of Ca++ per kilogram of body weight per minute). The experiment consisted of three successive 15 minute control periods, followed by three 15 minute calcium gluconate infusion periods and two 15 minute recovery periods. During calcium gluconate infusion, mean serum Ca++, and ECa++, ENa+, and EFNa+ from the infuses kidney increased (p less than 0.005). Systolic blood pressure (142 mm. Hg +/- 8S.E.), renal blood flow (137 ml. per minute +/- 11 S.E.), creatinine clearance, and aldosterone excretion (12.0 ng. per 15 minute +/- 1.5 S.E.) did not change (p less than 0.3). Renal venous PRA (28.4 ng. per millileter per hour +/- 7.5 S.E.) decreased (p less than 0.014). The per cent decrease of PRA correlated (r = -0.70) with the per cent increase EFNa+ (p less than 0.001). Calcium gluconate had a lesser (p less than 0.01) inhibitory effect on renin than CaCl2, despite greater excretion of Ca++ and Na++ during calcium gluconate infusion. Taken together, the results indicate that Ca++ inhibits renin release, although the extent of the inhibition is modified by the anion accompanying Ca++. The effect of Ca++ on renin may be mediated by NaCl transport across the macula densa.