The limitations of "vulnerability" as a protection for human research participants.

This article examines the concept of vulnerability in research ethics, and discusses how different regulations and policy documents have dealt with the concept of vulnerability, either as an inability to give informed consent or emphasizing unequal power relationships between politically and economically disadvantaged groups and investigators or sponsors. Because so many groups are now considered to be vulnerable, the term has lost its force, and it may not adequately protect certain subjects from harm. The author calls for the use of regulation to protect these groups, but also for researchers to pay attention to characteristics of the research protocol and environment that present ethical challenges.