This article employs the notion of legitimation strategy in new religious movements to explore and compare the use of scientific rationales and language in Christian Science and the Unity School of Christianity. I examine how Christian Science and Unity used science to present their beliefs and practices, and I focus on Christian Science testimonials and Unity's advocacy of vegetarianism to demonstrate their reliance upon scientific epistemologies. I argue that the two movements used scientific rationales and language as a strategy to validate themselves in late nineteenth-century and early twentieth-century America, which had largely accepted the scientific worldview as a primary source of knowledge about the world. A key difference in the way they used science helps to explain the vastly different levels of social controversy involving the two movements.