This working paper presents the findings of copy test research on consumer perceptions of food and dietary supplement print advertisements containing qualified health claims for diet-disease relationships that lack a high level of scientific support. The research was motivated by court decisions that struck down the Food and Drug Administration’s outright ban on such claims in labeling. The decisions effectively have placed the burden on the government to allow qualified claims for these diet-disease relationships unless it can demonstrate that consumers are unable to understand qualifications characterizing the true level of certainty in the relevant scientific evidence. My findings indicate that qualified language can have a significant impact on consumer evaluation of scientific certainty. My research also suggests, however, that it will be a difficult task to craft qualifications in advertising that communicate a low level of scientific certainty. None of the tested disclaimers, whether appearing in real advertisements for real products or in fictitious advertisements, communicated serious limitations in scientific evidence (i.e. science that FDA would rate at a “D” level). In addition, consumers interpreted all of the tested advertisements in widely disparate fashion. For example, although consumers seeing an ad for a fictitious antioxidant vitamin supplement on average rated the degree of scientific evidence correctly at a “C” level of support, approximately two-thirds of the consumers either overestimated or underestimated the certainty of the science.