A chromosomal DNA fragment from Vibrio cholerae non-O1 containing a drug resistance determinant was cloned and sequenced. The deduced amino acid sequence suggested that the determinant gene encodes a multidrug efflux pump. We designated the pump VcmA. Escherichia coli cells transformed with a plasmid carrying the vcmA gene showed increased resistance against norfloxacin, ciprofloxacin, ofloxacin, daunomycin, doxorubicin, streptomycin, kanamycin, ethidium bromide, 4',6-diamidino-2-phenylindole dihydrochloride, Hoechst 33342 and acriflavine. Na+ (or Li+)-dependent efflux of ethidium bromide was detected in transformant cells. Efflux of Na+, elicited by ethidium bromide, was observed from transformant cells. Thus, we concluded that the VcmA is a Na+/drug antiporter.