Besides children, numerous other types of subjects require special attention when obtaining informed consent. In all cases, the guiding principle is respect for the rights of the potential subject. Federal regulations consider prisoners, the mentally disabled, and pregnant women to be "special populations," and as such, are entitled to extra protection under the law. Other groups, such as racial minorities, the elderly, substance abusers, the economically disadvantaged, the very sick and the institutionalized are described as "vulnerable populations" and are extended similar protection when used as research subjects. Researchers wishing to use these populations as research subjects must contact the IRB Chair prior to protocol submission in order to determine what, if any, additional restrictions may be imposed in order to assure the protection of subjects falling in the special/vulnerable populations category.