When environmental health researchers study hazards in the home, they often discover information that may be relevant to protecting the health and safety of the research subjects and occupants. This article describes the ethical and legal basis for a duty to warn research subjects and occupants about hazards in the home and explores the extent of this duty. Investigators should inform research subjects and occupants about the results of tests conducted as part of the research protocol only if the information (...) is likely to be accurate, reliable, and medically useful. Investigators should warn subjects and occupants about hazards they happen to discover while they are in the home, if a reasonable person would warn the subjects and occupants about those hazards. Investigators should not report illegal hazards discovered in the home to the authorities, unless those hazards constitute abuse or neglect of children or mentally disabled people living in the home. When investigators decide to warn research subjects and occupants about hazards in the home, they should take some steps to help them make effective use of this information, such as providing additional counselling or making a referral for remediation or medical treatment. Investigators should discuss these issues with research subjects during the informed consent process. (shrink)