Science provides the most important set of tools for the evaluation of complementary and alternative medicine (CAM). Nonetheless, there are important limits in science that constrain its ability to evaluate CAM effectively. Some are the limits encountered by science in conventional medical research. Others are peculiar to this controversial topic. The most important limits are not those inherent within the basic methods of science, but rather within the culture of science — the particular ways that scientific knowledge, theory, and method are configured and arrayed rhetorically, and in the social context in which science operates. It is the limitations of scientists as a group of human beings more than science as a set of methods that hamper scientific evaluation of CAM.