Some are concerned about the possibility that offering money for research participation can constitute coercion or undue influence capable of distorting the judgment of potential research subjects and compromising the voluntariness of their informed consent. The author recognizes that more often than not there are multiple influences leading to decisions, including decisions about research participation. The concept of undue influence is explored, as well as the question of whether or not there is something uniquely distorting about money as opposed to (...) a chance for treatment or medical care. An amount of money that is not excessive and is calculated on the basis of time or contribution may, rather than constitute an undue inducement, be an indication of respect for the time and contribution that research subjects make. (shrink)