This article examines the medical activism of the New York physician Mary Putnam Jacobi (1842-1906), to illustrate the problems of gender and science at the center of the vivisection debate in late nineteenth-century America. In the post-Civil War era, individuals both inside and outside the medical community considered vivisection to be a controversial practice. Physicians divided over the value of live animal experimentation, while reformers and activists campaigned against it. Jacobi stepped into the center of the controversy and tried to use her public defense of experimentation to the advantage of women in the medical profession. Her advocacy of vivisection was part of her broader effort to reform medical education, especially at women's institutions. It was also a political strategy aimed at associating women with scientific practices to advance a women's rights agenda. Her work demonstrates how debates over women in medicine and science in medicine, suffrage, and experimentation overlapped at a critical moment of historical transition.