Inactivation mutations of the luminal thiazide-sensitive NaCl cotransporter (NCC) in the of distal convoluted tubules (DCT) or the basolateral chloride channel (CLCNKB) in distal nephron are the most common genetic mutations in Gitelman's syndrome (GS) or Bartter's syndrome (BS). We conduct the clinical and molecular studies in Chinese patients with GS or BS. Twenty patients with chronic hypokalemia (M/F = 15/5, age 25 ± 7) in 15 unrelated Chinese families were investigated. All had renal potassium (K⁺) wasting, metabolic alkalosis and normotension. The urinary calcium excretion rate was used to distinguish between GS or GS on clinical grounds. Clinical symptoms and biochemical studies were recorded. Molecular analysis included PCR (PCR)-single strand conformation polymorphism (SSCP), direct sequencing of both the NCC and CLCNKB genes, and restriction fragment length polymorphism (RFLP). Sixteen patients had a clinical diagnosis of GS with hypocalciuria and 4 BS without hypocalciuria. Four of these 20 patients did not have hypomagnesemia. The males had severe hypokalemia (1.9 ± 0.4 mEq/liter [mmol/liter]) with paralytic episodes whereas females had moderate hypokalemia (2.6 ± 0.2 mEq/liter [mmol/liter]) and less severe symptoms. There were no mutations detected in CLCNKB. Twelve NCC mutations including 6 novel mutations and 9 recurrent ones were identified. Allele frequency of the detected NCC mutations was 3% in 100 healthy subjects. Some GS patients with NCC mutations may have normocalciuria and/or normomagnesemia. Gender differences may account for phenotype variability. Screening of these identified NCC mutations remains as the ‘gold standard' for the diagnosis of GS.