Coagulation tests including platelet count, factor V assay, fibrinogen, fibrin split products, and serial thrombin time were performed on 51 patients with cancer. Elevated fibrin split products and/or abnormal serial thrombin time was present in 24 (48%) patients. Bleeding occurred in three patients; each had normal platelet counts. However, the serial thrombin time was not normal and/or increased fibrin split products were present. The data add support to the hypothesis that cancer patients do have a delicately balanced coagulation mechanism, and chronic disseminated intravascular coagulation may be induced or aggravated by various stimuli, including radiation therapy, chemotherapy, sepsis, and perhaps other unrecognized situations.