Cancer is often associated with abnormal activation of coagulation leading to a prothrombotic state. Some chemotherapeutic agents used for cancer may induce thrombosis but their biological alterations in the hemostatic system are not yet well understood. This study evaluated alterations of coagulative and fibrinolytic parameters following chemotherapy. In plasma samples of 38 patients (median age: 49 years) receiving CMF (schedule 1-21 or 1-8) for Stage II breast cancer, we evaluated: PT, aPTT, antithrombin III (AT-III), protein C (PC), protein S (PS), thrombin-antithrombin complex (TAT), prothrombin fragment F 1 + 2 (F 1 + 2), fibrinogen (Fbg), tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1) and D-dimer (D-D). PT, aPTT, and Fbg were determined with routine methods; AT-III, PC, and PS were measured with coagulative tests; PC and PS were also evaluated with immunoenzymatic methods, t-PA, PAI-1, D-D, TAT, and F 1 + 2 were measured with immunoenzymatic methods. All tests were performed immediately before starting therapy and after each cycle. A PC antigen decrease appeared soon after beginning therapy and lasted throughout chemotherapy. The lowest values were present after the first treatment both in the CMF 1-21 group (mean +/- SD = 72.5 +/- 10.8%) and in the CMF 1-8 group (mean +/- SD = 77.2 +/- 6.9%): PC activity was also decreased. PS antigen decreased after the first administration (mean +/- SD = 73.3 +/- 10% in CMF 1-21 group, and 72.5 +/- 4.9% in CMF 1-8 group): PS activity also decreased. PAI-1 antigen levels increased (mean +/- SD = 43.1 +/- 20.4 ng/ml in the CMF 1-21 group, and 37.5 +/- 12.2 ng/ml in CMF 1-8 group) lasting up to the last cycle. CMF provokes a trend toward hypercoagulability; this effect should be considered when chemotherapy is employed in advanced cancer patients at high risk for thrombosis, or in patients with other risk factors.