Philip Curtin has devoted considerable study to disease by using military health statistics to calculate the 'relocation cost' of empire - the increased mortality caused by movement between disease environments. On all sides of the imperial conquest, migrants faced unfamiliar geographical, social and epidemiological environments that exacted tolls that were often harsh and too often fatal. So far, Curtin's relocation costs have been used only to measure the health effects on European troops and other long-distance migrants as they encountered new disease environments. This essay bridges a historiographical gap separating studies of European movements to Africa and intra-continental African labor migrations. At its core, relocation cost are relational measurements that mark changes across continents, climates and centuries. Curtin's approach focuses on divergent disease environments' effect on uniform populations. Drawing on the Office du Niger settlement scheme in central Mali, I demonstrate how this radically altered physical, human and disease environment affects the applicability of Curtin's relocation costs as a historical tool. Extant colonial medical data does not allow for comparisons between home and host disease environments, but the controlled environment of labor and tenant farming at the Office du Niger offers detailed morbidity statistics for those who came to the project. Taking an epidemiological approach, I will study the human dynamics and social differentiations within the disease environment. Finally, I will suggest an alternative single-site baseline and an integrative use of qualitative and quantitative sources to measure the social environment of disease among African workers in regional migration systems.