In the opening salvos of the First World War, a British Commission bemoaned the skyrocketing incidence of bilharzia (schistosomiasis) infection in Egypt. War sparked the fear that British soldiers stationed in Egypt might contract the infection and laid bare the weakened bodies of Egyptian agricultural laborers. While bilharzia was endemic in Egypt, the construction of the 1902 Aswan dam and its production of a new agricultural geography transformed the disease. Intensified agricultural labor regimes literally submerged vast numbers of Egyptian agricultural laborers in infected irrigation water. Experiences of the relationship between human and parasite became ever more painful, frequent, and fatal. Following the war, the British administration initiated a treatment campaign to fight bilharzia. In the 1920s, the new Egyptian government expanded the numerical and geographical reach of the bilharzia treatment program. During this period, officials at the Egyptian Ministry of Public Health estimated that nine to ten million of Egypt’s 13 million inhabitants were infected with bilharzia. Between 1920 and 1923, treatment annexes administered treatment to approximately 500,000 Egyptians. In 1927, the Rockefeller Foundation joined forces with the Egyptian government in their efforts to combat bilharzia. Drawing from a wide array of archival sources from the Egyptian Ministry of Public Health and the archives of the Rockefeller Foundation, this paper explores endeavors to imagine, thwart, and treat bilharzia infection during the interwar period in Egypt. The first portion of the paper chronicles the troubled imaginations of bilharzia among scientists, medical practitioners, and those infected. A diverse realm of material encounters with the environment at large fed these imaginations. During this period, treatment regimens were brutal and often ineffective, agricultural labor regimes assured the continual reinfection of laborers, and measures to combat the disease were centered on largely irrelevant “sanitation” campaigns in Egyptian villages. The second portion of the paper traces bilharzia’s nature as a fundamentally situated phenomenon. Efforts to transport the schistosome abroad for research met with failure. Live samples perished so frequently that a Rockefeller scientist, Claude Barlow, infected himself with the disease before travel in order to carry the parasite overseas. Both as a matter of treatment and as an object of research, bilharzia was intimately tied with a web of material relationships rooted in the specificity of the Egyptian environment.