Research and development has been supported by the U.S. Environmental Protection Agency (EPA) since 1990 to investigate the feasibility of using biological methods based on human, animal, or in vitro responses to characterize sources of indoor air emissions. The “bioresponse” methods being evaluated measure odor and sensory irritation of mucosal tissues in the eyes, nose, and upper airways. Chambers for creating controlled emissions from sources are basically the same as have been used for traditional studies of emission rates and chemical compositions. Studies of human subject responses to known odorous or sensory irritant chemicals using nose-only, eye-only, facial, and whole-body exposures are providing baseline data against which animal and in vitro results will be validated. The animal and in vitro methods being investigated measure changes in respiratory patterns and chemosensory evoked potentials. The status of current and future projects is reported.