To investigate the extent to which personal values and experiences among scientists might affect their assessment of risks from dioxin, radon, and environmental tobacco smoke (ETS), we conducted an experiment through a telephone survey of 1461 epidemiologists, toxicologists, physicians, and general scientists. Each participant was read a vignette designed to reflect the mainstream scientific thinking on one of the three substances. For half of the participants (group A) the substance was named. For the other half (group B), the substance was not named but was identified only as Substance X, Y, or Z. Knowing the name of the substance had little effect on the scientists’ evaluation of dioxin, although those who knew the substance to be dioxin were more likely to rate the substance as a serious environmental health hazard (51% vs. 42%,p= 0.062). For radon, those who knew the substance by name were significantly more likely to consider it an environmental health hazard than were those who knew it as substance Z (91% vs. 78%,p<0.001). Participants who knew they were being asked about ETS rather than substance X were significantly more likely to consider the substance an environmental health hazard (88% vs. 66%,p<0.001), to consider the substance a serious environmental health hazard (70% vs. 33%,p<0.001), to believe that background exposure required public health intervention (85% vs. 41%,p<0.001), and to believe that above‐background exposure required public health intervention (90% vs. 74%,p<0.001). These findings suggest that values and experiences may be influencing health risk assessments for these substances, and indicate the need for more study of this phenome