SUMMARY
The excretion of phosphate in the rat after renal infusion of parathyroid hormone or cyclic adenosine 3,′5′-monophosphate (AMP) is described. The hormone stimulated an immediate phosphaturia, but no such response was measurable in the presence of cyclic AMP. Adenyl cyclase activity in kidney cortex was assessed by measuring the conversion of [14C]adenosine 5′-triphosphate to [14C]cyclic AMP. Previous infusion of kidneys with parathyroid hormone did not alter adenyl cyclase activity but the addition of the hormone to kidney tissue in vitro caused a significant increase in the activity of this enzyme. It is suggested that the parathyroid hormone-stimulated phosphaturia is not mediated by cyclic AMP.