This paper demonstrates how British Quakers, between 1870 and 1914, attempted to understand and debate the issue of vivisection through the lens of the Quaker peace testimony. Drawing on primary source materials, the article argues that these Friends were able to agitate for radical legislative and social change using virtue ethics as their framework. The paper further suggests that the moral parameters of the Quaker testimony for peace expanded briefly in this period to include interspecies as well as intraspecies engagement. Friends accomplished this by arguing that humans could not engage in vivisection—a “moral disease” just like slavery and war—without risking individual and social virtue. Friends were able to call for radical change in society without arguing for ethical egalitarianism. Hierarchy was implicit in their virtue ethic, but this did not hinder their creation of a forward-thinking stance on human-animal relations.