In 38 patients with deep venous thrombosis and 52 patients with myocardial infarction who were on long term anticoagulant therapy, the estimations of β-TG have been done by radioimmunoassay using a kit developed by the Radiochemical Centre, Amersham, England. In the group of patients with deep venous thrombosis, the increased values of β-TG /values which were higher than 80 ng/ml /have been established in 47,3% of the cases and among the patients with myocardial infarction, in 73% of the cases. From the total of 56 patients with increased level of β-TG, in 50 patients the level of prothrombin activity was higher than 20%. On the other hand, in patients with normal concentration of β-TG, the level of prothrombin activity was usually lower than 20%. Our preliminary results suggest the possible use of estimation of β-TG as an important supplementary parameter for evaluation of a substantial efficasy of applied anticoagulant therapy.