SummaryThe response to parathyroid hormone (PTH) and calcitonin (CT) was studied in eight children with various bone diseases by determining the serum calcium (Ca) and phosphate (P) concentration, urinary phosphate excretion rate, renal phosphate clearance, the percentage of filtered phosphate reabsorbed by the renal tubule (%TRP), creatinine clearance (Ccr), urinary cyclic adenosine 3′,5′ monophosphate excretion rate (UcAMPV), and urinary cyclic guanosine 3′,5′ monophosphate excretion rate (UcGMPV). Administration of PTH caused no significant change in serum Ca and P values, whereas CT produced a decrease in Ca (Δ Ca, −1.4 ± 0.1 mg/100 ml) and P (ΔP; −1.1 ± 0.1 mg/100 ml). There was an increase in UcAMPV (ΔUcAMPV; 437 ± 74 nmoles/min/100 ml Ccr) without any significant change in UcGMPV after administration of PTH. Phosphaturia was produced by both PTH (Δ TRP, −18 ± 3%) and CT (ΔTRP, −13 ± 2%). However, CT did not elicit any increase in either UcAMPV or UcGMPV.SpeculationParathyroid hormone (PTH) and calcitonin (CT) induce phosphaturia of a similar magnitude whereas PTH alone increased the urinary excretion of cyclic adenosine 3′,5′ monosphosphate (cAMP). The phosphaturia induced by CT may not be mediated by a similar mechanism involving the adenylate cyclase-cAMP system as demonstrated for PTH.