A gene encoding an Na+/H+ antiporter was cloned from vibrio parahaemolyticus into the plasmid pBR322 and expressed in Escherichia coli cells. The gene enabled mutant E. coli cells to grow in the presence of 0.2 M NaCl (or 10 mM LiCl). These cells were originally unable to grow under such conditions because of the lack of major Na+(Li+)/H+ antiporters. We detected Na+/H+ antiporter activity due to the gene in membrane vesicles. The gene was sequenced and the deduced amino acid sequence was found to be 72% identical to the NhaB Na+/H+ antiporter of E. coli.