Factors influencing guanosine 3′5′-monophosphate (cGMP) metabolism were examined in slices of rat renal cortex, outer medulla, and inner medulla. In the presence of extracellular Ca 2+ and O 2, a gradation of steady-state cGMP levels was evident among the tissues (inner medulla outer medulla cortex). Carbamylcholine, bradykinin, histamine, and the divalent cation ionophore A23187 significantly increased cGMP in each tissue. The cGMP-stimulating action of these agents was reversibly abolished by exclusion of either Ca 2+ or O 2. The influence of Ca 2+ and O 2 on expression of effects of carbamylcholine and related cGMP agonists was interdependent in each region of the kidney, since both were required for expression of agonist action. By contrast, nitrite, nitroprusside, NH 2OH, and nitrosoguanidine increased cGMP in the presence or absence of Ca 2+ or O 2. Thus, at least two distinct mechanisms for altering cGMP accumulation are operative or expressible in each region of the kidney: one that requires and one that does not require the presence of extracellular Ca 2+ and O 2. Results also suggested a role for transmembrane transport of Ca 2+ in the maintenance of basal cGMP and in the expression of the responses to Ca 2+-dependent agonists in renal cortex, outer and inner medulla. Thus, verapamil, which can block such transport, lowered basal cGMP and abolished these responses while ionophore A23187 enhanced cGMP in cortex and medulla only in the presence of Ca 2+. The interrelationship of Ca 2+ and O 2 in control of basal cGMP levels clearly differed in cortex compared to inner medulla. In cortex, Ca 2+ and/or O 2 deprivation produced quantitatively similar reductions in cGMP. Moreover, expression of the action of O 2 to increase cortical cGMP required Ca 2+. Thus, O 2 effects on cGMP in cortex were closely coupled with or mediated through Ca 2+. By contrast, in inner medulla, O 2 deprivation resulted in more pronounced reduction in basal cGMP than did Ca 2+-deprivation, and O 2 significantly increased inner medullary cGMP in the absence of extracellular Ca 2+. The latter indicates that the action of O 2 to increase cGMP in inner medulla is not totally interdependent with that of Ca 2+. In inner medulla, Ca 2+ or O 2 deprivation had effects on cAMP accumulation that were analogous to those on cGMP, whereas exclusion of extracellular Ca 2+ had no detectable effect on cAMP in cortex. Accordingly, common or related cellular processes may operate in control of accumulation of both cGMP and cAMP in inner medulla.