Determinations of thrombin/antithrombin III complex (TAT) in human plasma with the new enzyme immunoassay (Enzygnost-TAT) were performed. The study group consisted of 36 patients aged 36-79 years suffering from peripheral obliterative arterial disease (POAD) comparing to control group. In patients the elevation of TAT level was detected. The analysis of increased TAT level in the relation to clinical atherosclerotic complications, the kind of treatment, the stage of POAD, the age of patients and the period after operation was done. The highest TAT complex seemed to be correlated with the advance of atherosclerotic process, with additional diseases such as arterial hypertension, diabetes mellitus and performed operation. The "Enzygnost-TAT" assay can be useful for the detection of prethrombotic states without clinical symptoms of hypercoagulability and can be applied for clinical diagnosis.