Malignant hematologic disorders may be associated with coagulopathy causing bleeding or thromboembolic complications. Severe infections as well as chemotherapy may augment this risk by the action of inflammatory mediators and the release of proteases. We evaluated the hemostatic process in 10 patients with acute myeloid leukemia (no acute promyelocytic leukemia) before the start of induction therapy with IDA-C and daily during the following two weeks of treatment. Various hemostatic parameters were studied, including the complex between activated protein C and the protein C inhibitor (APC-PCI) with a newly developed method, thrombin generation, protein C, prothrombin fragment 1+2 (F1+2), antithrombin and factor VIII. The APC-PCI concentration was relatively high in all patients at start of treatment (mean 0.81 ± SEM 0.27 μg/L; normal range 0.07–0.26 μg/L) reflecting an activation of the coagulation system, and further increased during the initial phase of chemotherapy reaching the highest level on Day 3 to 5 of 1.67±0.53 μg/L (p=0.0047). The concentration of the complex then declined during the following 10 days to 0.10±0.03 μg/L on Day 14, i.e. to a concentration significantly lower than that at start of treatment (p=0.005). The concentration of F1+2 varied in a similar way with a concentration of 2.17±0.51 nM at start of treatment and an increase on Day 3–5 to 4.17±0.93 nM (p=0.005) followed by a decline to 1.09±0.22 nM on Day 14. Thrombin generation was relatively high in the initial phase of chemotherapy (319.0±44.5 nM) and then declined to 154.6±17.2 nM on Day 14 (p=0.008). The protein C activity was relatively low at start (0.70±0.05 IU/mL) indicating a state of consumption, but showed a trend towards normalization during treatment reaching an average level of 0.78±0.05 IU/mL for all patients on Day 14 (p=0.103). The factor VIII level was high and relatively stable during the two weeks of treatment with a range of 1.73±0.16 to 1.89±0.17 IU/mL, indicating a reactive state. The level of antithrombin was normal at start of treatment (1.00±0.05 IU/mL) and throughout the study period. Our data show that acute myeloid leukemia may be associated with a significant coagulopathy and that the activity in the coagulation process is increased during the initial phase of chemotherapy. This should be considered in patients at start of treatment, in particular, in patients with septicemia and/or signs of disseminated intravascular coagulation.