D-dimers (D-d) are degeneration products of fibrin. According to some recommendations (Lee et al., Ann Rev Med, 2002; 53: 15-33) the vein thromboembolism may be excluded by the determination of D-dimers level especially when the probability of diagnosis of deep vein thrombosis is less strong. The determination of D-dimers with made possible was the development of monoclonal antibodies and their detection is based on the determination using the principle of ELISA or agglutination techniques. An increased D-d level is not completely specific for venous thrombo-embolism; it may be enhanced during tumorous diseases, infections, kidney failure etc. In contrast, a negative result of the test is highly sensitive for exclusion of deep vein thrombosis or pulmonary embolism (sensitivity 90% to 100%). The authors also present their own results of a prospective study on the dynamism of D-dimer level in plasma of patients with deep vein thrombosis demonstrated by sonography at the time of start and in the course of the anticoagulant therapy. D-dimers were determined by two methods, the quantitative agglutination latex method and the rapid VIDAS ELISA method. At the time of admission, an increased level was established in up to 80% of patients using the VIDAS method and in 70% using the latex method. In the period of five to seven days after the beginning of treatment the proportions were 75% and 60%, respectively, according to the method used. After six weeks, a slightly elevated level above normal may be expected in 1/3 of patients and less than in 1/5 of patients in the later months.