The disparity in resources between economically developed and developing countries presents ethical concerns when commercial sponsors of studies and investigators propose to conduct them with subjects in developing countries. Vulnerable people may be recruited into studies of little health benefit to themselves or their communities and, under undue inducements, may accept disproportionate risks. Reproductive health studies may present women with undue risks. Guidelines have been developed to protect exploitable populations in resource-poor settings, although guarding their right to make informed and voluntary choices poses special challenges. Guidelines pay special attention to pregnant women as research subjects, and may approve and even require their enrollment in studies of products not known to be harmful. Placebo-controlled studies are addressed in contexts where no recognized treatments are routinely accessible. The structure and functions of research ethics review committees present difficult challenges, but they may be mitigated by enlightened international collaboration.