Allied prisoners of war (POWs) working on the Imperial Japanese Army's railroad from Thailand to Burma during 1943-1945 devised a blood transfusion service to rescue severely ill fellow prisoners who were otherwise unlikely to survive the war. Extant transfusion records (1,251 recipients, 1,189 donors) in ledger books held by the United Kingdom National Archives at Kew were accessed and analyzed. Survival to the end of the war in 1945 was determined from Commonwealth War Graves Commission records. The records examined indicate that freshly donated whole blood was manually defibrinated and transfused after crossmatches based on POW medic sera. Overall survival to the end of the war was 74% in recipients and 88% in donors. Postwar survival rates were significantly higher for transfusion recipients with malaria (89.3%) than for other diagnoses: 52.6% for malnutrition, 59.3% for dysentery, 67.2% for skin ulcers, and 75.4% for other causes (odds ratio: 3.97; 95% CI: 2.79-5.28; P <0.0001). By 1945, the vast majority of blood transfusions were given for severe anemia caused by chronic relapsing vivax malaria. Although the POW situation was admittedly extreme, our data provide evidence that blood transfusions to treat severe anemia were associated with higher survival among patients with Plasmodium vivax infection than among those with other morbidities.