This article examines scientific transnationalism as an art of engagement with, and avoidance of, the threats and promises of what was foreign to the nation. Portuguese racial anthropologists experienced a tension between remaining imperial-nationalistic in character, and internationalist in their activities simultaneously. They struggled to exclude foreigners from colonial field sites; they aimed at nativist authority based on total control of colonial data. Yet, they eagerly sought connections with foreign experts to capitalize provincial scientific authority within Portugal’s colonies. The essay conceptualizes this mode of transnationalism as also a kind of isolationism, an inward oriented form of engaging with foreign sciences and scientists as ambivalently powerful and threatening strangers.