Inherited renal tubular disorders associated with hypokalemic alkalosis (Bartter-like syndromes) can be subdivided into at least three clinical phenotypes: (i) the hypocalciuric-hypomagnesemic Gitelman variant; (ii) the classic variant; and (iii) the antenatal hypercalciuric variant (also termed hyperprostaglandin E syndrome). Mutations in the Na-Cl cotransporter (NCCT) underlie the pathogenesis of the Gitelman variant and mutations in the Na-K-2Cl cotransporter (NKCC2) have recently been identified in the antenatal hypercalciuric variant. We now describe mutations in the gene encoding the inwardly-rectifying potassium channel, ROMK, in eight kindreds with the antenatal variant of Bartter syndrome. These findings indicate that antenatal Bartter syndrome is genetically heterogeneous and provide new insights into the molecular pathogenesis of Bartter-like syndromes.