Comparative clinical and experimental investigations were carried out on 18 clinically normal horses. It was found that the single transfusion of in vitro UV-treated autogenous blood, following a previously described method, was tolerated well by horses and did not lead to any deviations from the normal indices. Under the effect of the treated blood there was an increase in the hemoglobin content, rise in the erythrocyte and leukocyte count with slightly expressed hyperleukocytosis and weak neutrophilia (simple regeneration of the blood). The sedimentation of erythrocytes also showed higher rates as early as the first hour following the autohemotransfusion, remaining at the attained level up to the fourth day, while on the sixth day it again came back to the initial value. The contents of calcium and inorganic phosphorus rose, showing a slightly expressed shift to the physiologic level without reaching it. The changes in the phagocytic activity of the blood showed that the autohemotransfusion stimulates phagocytosis. Along with these effects the bacteriostatic titer of the blood, as recorded with the use of the anthrax bacillus as early as the first hour, and likewise favourably affected, the highest titers being observed at the 24th and 48th hour.