Nearly 100 years ago, Ashworth2reported the finding of cancer cells in the blood of a dead patient similar to those of the patient's malignant skin tumor. In 1934, Pool and Dunlop11studied the systemic blood of patients with cancer for presence of neoplastic cells, and Engell5in 1955 discovered tumor cells in the peripheral blood of patients with resectable and unresectable neoplasms. In the last 4 to 5 years, because of the development of new cytologic methods, more reports have appeared in the literature on the presence of cancer cells in the blood of patients with resectable neoplasm. This led to the use of chemotherapeutic agents at the time of surgery in an attempt to affect the cancer cells in the systemic circulation.10,13 In our laboratory we have been investigating the effects of alteration of the clotting mechanism on the production of tumor metastases. Fibrinolysin