Three principal factors affect the stringency of medical researchers' obligation to provide antiretroviral treatment to participants in non-HIV/AIDS studies that are conducted in developing countries: (1) the centrality of HIV/AIDS to the study design, (2) the extent of the researcher-participant interaction, and (3) the cost relative to the study budget. I provide a basis for assessing the comparative stringency of the researchers' obligation to provide this type of ancillary care. Practically, given the range of possible responses to study participants' needs, calibrating the researcher's responsibility to provide ancillary care is a useful step in ethical analysis. Theoretically, a gradation of obligation suggests how research ethics committees or institutional review boards can take multiple, potentially conflicting ethical factors into account without undertaking spurious efforts to quantify their importance.