The kidney plays an important role in maintaining the systemic Ca 2+ and Mg 2+ balance. Thus the renal reabsorptive capacity of these cations can be amended to adapt to disturbances in plasma Ca 2+ and Mg 2+ concentrations. The reabsorption of Ca 2+ and Mg 2+ is driven by transport of other electrolytes, sometimes through selective channels and often supported by hormonal stimuli. It is, therefore, not surprising that monogenic disorders affecting such renal processes may impose a shift in, or even completely blunt, the reabsorptive capacity of these divalent cations within the kidney. Accordingly, in Dent's disease, a disorder with defective proximal tubular transport, hypercalciuria is frequently observed. Dysfunctional thick ascending limb transport in Bartter's syndrome, familial hypomagnesaemia with hypercalciuria and nephrocalcinosis, and diseases associated with Ca 2+ -sensing receptor defects, markedly change tubular transport of Ca 2+ and Mg 2+ . In the distal convolutions, several proteins involved in Mg 2+ transport have been identified [TRPM6 (transient receptor potential melastatin 6), proEGF (pro-epidermal growth factor) and FXYD2 (Na + /K + -ATPase γ-subunit)]. In addition, conditions such as Gitelman's syndrome, distal renal tubular acidosis and pseudohypoaldosteronism type II, as well as a mitochondrial defect associated with hypomagnesaemia, all change the renal handling of divalent cations. These hereditary disorders have, in many cases, substantially increased our understanding of the complex transport processes in the kidney and their contribution to the regulation of overall Ca 2+ and Mg 2+ balance.