The history of leprosy treatment among the Karo of Sumatra illustrates how leprosy afforded missionaries an evangelistic opportunity, and how that opportunity eroded in the twentieth century with changing therapies for the illness. Because it symbolized Christian charity, leprosy care drew donations and support for the missionary movement of the nineteenth century. In Karoland, as elsewhere, leprosy patients were attracted to the missionaries' religion because therapy entailed separation from kin and community and then incorporation into a new kind of community, an asylum, where the authority structure, the dispensation of resources, and the constructed spaces of everyday life made the idea of a supreme deity an experienced reality. When therapies of leprosy shifted to an out-patient system, one of the older missionaries to the Karo struggled to maintain control of the leprosarium that had been one of the few pockets of conversion in this mission field.