Acute effects of salmon calcitonin (CT) on renal electrolyte excretion were investigated in intact, thyroparathyroidectomized (TPTX) and uremic rats. Glomerular filtration rate did not change during CT infusion and there was no volume expansion in any experimental group. Plasma calcium levels gradually fell below the control period in each experimental group. Urinary calcium excretion increased at the early period in both intact and TPTX rats but fell below the control period with the continuous infusion of CT. In uremic rats, a decrease in plasma calcium was followed by a decrease in calcium excretion. Plasma phosphate gradually decreased and simultaneously measured phosphate excretion increased in both intact and TPTX rats. In uremic rats, however, there was no change in phosphate excretion and only a slight decrease of plasma phosphate. Phosphaturia is the result of the predominant renal action of CT and occurs even when the filtered load of phosphate decreases. In uremic animals, there appears to be a resistance to exogenous CT which manifests itself by the absence of natriuretic, calciuric and phosphaturic responses.