© 2014, Johns Hopkins University Press. All rights reserved. The adoption of the cowpox vaccine in nineteenth-century Japan has often been seen as a more straightforward development than its introduction to other non-Western countries. However, the research leading to this conclusion has been based primarily on sources written by Japanese practitioners of Western- style medicine (ran), while the perspectives of Chinese-style (kan) practitioners, who were more numerous than ranpō practitioners but less likely to have shown immediate enthusiasm for vaccination, have been largely neglected. Kanpō doctors typically learned about vaccination from Chinese rather than European sources and often held an ambivalent attitude toward the vaccine’s foreign origins. This article develops an analysis of kanpō writings on vaccination and suggests that skepticism about the vaccine remained widespread for at least a decade after its initial arrival in Japan, providing new insights into both the initial opposition and the subsequent acceptance of the technique. ; published_or_final_version