The recent flood of research concerning pollutants in personal environmental and biological samples-blood, urine, breastmilk, household dust and air, umbilical cord blood, and other media-raises questions about whether and how to report results to individual study participants. Clinical medicine provides an expert-driven framework, whereas community-based participatory research emphasizes participants' right to know and the potential to inform action even when health effects are uncertain. Activist efforts offer other models. We consider ethical issues involved in the decision to report individual results in exposure studies and what information should be included. Our discussion is informed by our experience with 120 women in a study of 89 pollutants in homes and by interviews with other researchers and institutional review board staff.