In the early 20th century, colonial Tunisia’s Gafsa phosphate mines enabled capital-intensive farming in Europe. The French-owned Gafsa Phosphate and Railway Company (CPCFG) exported millions of tons of phosphate rock to European fertilizer factories, making Gafsa the world’s largest phosphate exporter through the end of the 1920s. Combining doctor’s reports, biomedical research papers, and oral histories—and merging approaches from social history, environmental history, and history of science—I argue that 1920s contestations around occupational disease in Gafsa folded the region into global networks of biomedical knowledge, with enduring consequences through the following decades. These biomedical networks were both a cause and a consequence of Gafsa’s integration into global capitalist markets, because they reflected capitalism’s imperative of devaluing colonial labor. The CPCFG’s power to extract profits—from the minerals under Gafsa’s mountains and the labor power of Gafsa’s residents—relied on its ability to define which diseases were “of the workplace” and which ones weren’t. But the survival strategies that Gafsa’s residents developed to cope with pollution and illness emerged from the reality that “the workplace” never fell within distinct boundaries. The CPCFG had to work constantly to claim authority over where “the workplace” ended, and in doing so, it situated Gafsa within transnational circuits of biomedical knowledge. Company doctors and colonial researchers drew on international debates about silicosis in the 1920s and 1930s to imagine phosphate dust as harmless. They used Gafsa as a laboratory to argue that cancer was a disease of Europe, not of the colonies, crafting a modernization theory of disease that still pervades global public health today. Throughout, workers and their families sought to prove that their maladies stemmed from “a known occupational disease,” both co-opting and challenging the existing public health consensus. Their arguments merged biomedical claims with other ways of knowing, both environmentally embedded and embodied. Labor history is global not only because of migration, the transnational left, and the circulation of produced goods, as other scholars of the Middle East and North Africa have shown. Rather, labor’s embodied dynamics also unfolded on a global scale, shaped by contestation among capitalists, doctors, workers, and their families over ways of knowing occupational disease. By viewing histories of labor and public health together, we not only reach a better understanding of the global scales within which capitalism’s cheapening of labor unfolded, but we also gain insight on the colonial-industrial roots of contemporary public health paradigms.