Korean hemorrhagic fever is a disease with an acute onset of severe hemorrhagic tendency and acute renal failure. Acute renal failure may be produced by inducing intravascular coagulation in experimental animals, and also, coagulation mechanisms may play a pathogenetic role in certain human renal diseases. One of the clinical consequences of DIC is serious ischemic tissue damage due to capillary flow blocking by fibrin deposits. The kidney is particularly vulnerable to ischemic effects. For the detection of intravascular coagulation, FDP assay is known as a more sensitive and reliable test than are other coagulation studies. Therefore, from September, 1973 to January, l974, the serum and the urine of the selected patients with Korean hemorrhagic fever who had a typical clinical course were subjected to study. The alterations of the serum and urinary FDP concentrations, and the other hematologic, blood chemistry, and urinary examinations were studied in a total of 177 examples of each febrile, hypotensive, oliguric, diuretic, and convalescent phase. Both the serum and urinary FDP concentrations were significantly higher than normal. This data indicates that DIC is detected in Korean hemorrhagic fever, where it may play a major pathogenetic role. And the urinary FDP concentration more closely reflects the severity of renal lesions in this disease than does the serum FDP concentration and the blood urea nitrogen level. It can be assumed that the concentration of urinary FDP can be used as a therapeutic criteria, and is correlated to the intensity and the prognosis of the disease. Also the possibility of improvement following anticoagulant treatment may be proposed. It appears that acute renal failure in this disease has a close relationship to DIC. In its pathogenesis it can be assumed that disruption of the renal cortical perfusion plays a major role in this Korean hemorrhagic fever.