Vibrio vulnificus produces Hemolysin/cytolysin (VvhA), which is one of the most potent exotoxins capable of killing mice at submicrogram levels. However, V. vulnificus growth and vvhA expression are severely repressed and extracellular VvhA produced at low levels is easily inactivated in human body fluids. This study was conducted to obtain additional unequivocal evidence of the enigmatic characteristic of VvhA. V. vulnificus growth was stimulated, vvhA expression was de-repressed, and extracellular VvhA production was increased in cirrhotic ascites, a human ex vivo experimental system, by a mutation of fur encoding ferric uptake regulator, which acts as a transcriptional repressor. However, regardless of the presence or absence of the for mutation, extracellular VvhA activity was not detected in cirrhotic ascites. These results indicate that VvhA is easily inactivated even when vvhA expression and extracellular VvhA production are maintained at high levels in cirrhotic ascites.