A case of refractory hypomagnesemia associated with hypokalemic alkalosis and hypocalciuria (Gitelman's syndrome) is described. The genetic mutations discovered to cause the hypokalemic alkalotic syndromes are described (the thiazide-sensitive sodium chloride co-transporter gene or TSC mutations in Gitelman's syndrome, and the sodium-potassium-chloride co-transporter gene or NKCC2 mutations in Bartter's syndrome). The molecular, electrolyte, and volume abnormalities are described, and the implications for diagnosis, therapy, and future research discussed.