This paper examines the threat to science from organized pseudoscience. It is easy to show that the general public's understanding of science is very poor. Therefore, determined people can advocate 'alternatives' to science which appear plausible to non-scientists. With skilful marketing, large sections of the public can be convinced that these alternatives should be taught in schools and universities, and that they merit funding for further research. The examples of creation science and intelligent design are considered. In both cases, the aim of these pseudo-sciences is to fundamentally alter the nature of science. Backed by large resources and vast numbers of supporters, it is suggested that movements like this can endanger science teaching and, eventually, the conduct of science itself. It is suggested that every scientist should be aware of the claims of these pseudo-sciences, and be in a position to offer basic refutations. In addition, it is necessary that specialists in the analysis and refutation of the pseudo-scientific claims should be available to offer further support.