A prethrombotic state is frequently reported in patients with cancer. Cytotoxic chemotherapy is also presumed to augment hypercoagulabilty. In this study, alterations in acute hemostasis were evaluated in 20 patients during chemotherapy. The pretreatment protein C and protein S activations were low in 15 (75%) and 16 (80%) patients, respectively. The fibrinogen level was high in 6 (30%) patients. The antithrombin III, fibrin degradation product (FDP) and plasminogen levels were in the normal range. During chemotherapy, no significant changes occurred in any of the parameters. These results indicate that chemiotherapy does not augment hypercoagulability in patients with cancer.