The isolation and functional characterization of a Candida albicans Na M /H M antiporter gene, CNH1, is reported here. The gene encodes a protein of 840 amino acids that exhibits high levels of similarity in sequence, size, and structural and functional domains to a group of known Na M /H M antiporters of fungi. The CNH1 gene is able to functionally complement the salt-sensitivity of a Saccharomyces cerevisiae ena1 nha1 mutant, and mutations of two conserved aspartate residues to asparagines in the putative Na M -binding site abolish this activity. Deletion of CNH1 results in retardation of growth and a highly elongated morphology in a significant fraction of cells under conditions that normally support yeast growth. These results indicate that CNH1 has a role in Na M and H M transport, salt-tolerance, and morphogenesis.