In experiments on nonanesthetized rats blood was substituted with perfluorotributyl emulsion (PFTBA). The mean volume of transfused PFTBA was 10 ml/100 g of body weight. During the period of blood replacement and the following 5 days the rats were kept in an atmosphere with increased oxygen content, and then they were placed under normal atmospheric conditions. The influence of PFTBA solution on hemopoiesis was studied in these experiments. A marked erythropoiesis activation in the bone marrow combined with expressed peripheral blood reticulocytosis was observed 6 days after the exchange blood substitution. Hemoglobin content decreased to 8.2 g% mature and immature white cell count rose; immature erythropoiesis cells were found: polychromatophilic erythro- and normoblasts (4.2% on the average). By the 13th day there was complete normalization of hemopoiesis which lasted 12 months without any significant deviations. Basing upon the results obtained it may be concluded that the PFTBA emulsion under study produces no negative effect on the animal hemopoiesis, and does not disturb the normal regulation process under conditions of the experiment conducted.