A comprehensive study of the hemostatic and coagulation mechanisms in 50 patients with disseminated malignancy was carried out. Significant laboratory abnormalities were found in the majority of patients. The most common pattern was the “hypercoagulable state.” This included short bleeding time, decreased silicone coagulation time and partial thromboplastin time, increased tolerance to heparin, marked elevation of plasma levels of factors I, II, V, VIII, IX and XI and acceleration of thromboplastin generation. There was elevation of platelet counts, except in patients receiving chemotherapeutic drugs. Seven patients had prolonged prothrombin time due to depression of vitamin‐K‐dependent clotting factors. Fibrinolysis was detected in six patients by immunologic and other techniques. The data suggest that patients with cancer have an alteration in the hemostatic level of control with increased levels of both clotting factors and their inhibitors, resulting in a more easily disturbed balance between opposing hemostatic forces. Clinical thrombosis or bleeding may follow.