Rheologic properties of red blood cells and hemostasis were studied in patients with acquired autoimmune hemolytic anemia who received antilymphocytic globulin (ALG). Hypocoagulation changes attended by elevation of red blood cell aggregation activity were detected in the patients already at their admission to the hospital. After administration of ALG, growth of these shifts, characteristic of disseminated intravascular blood coagulation (DIC) syndrome, was noted. It was shown that erythrocytic thromboplastin and antiheparin factor action on blood coagulation, mainly at the expense of the young cell fraction, was responsible for disorders in hemostasis. Nevertheless, despite the presence of DIC syndrome, in the group of patients, who received ALG, no clinical signs of this state were recorded, that could be explained by the protective effect of red blood cell intensified capacity for aggregation leading to the improvement of blood coagulation parameters.