It was established in an experiment with 13 sheep of the local improved breed that the single s/c injection of levamisole at the rate of 7.5 mg per kg of body mass led to a rise of the phagocytic activity of neutrophil leukocytes. These cells also had higher cytochemical activity of the alkaline phosphatase, glucose-6-phosphatase, and lipids (sudanophilia). No changes in the total count of leukocytes were found. The cytochemical activity of lactate-dehydrogenase, succinate-dehydrogenase, and alpha-glycerophosphate-dehydrogenase was also found to rise. On the base of the marker capacity of the acid naphthylacetate esterase with regard to the T-lymphocyte system there set in on the 3rd day following levamisole injection a 4 to 5 rise in the T-lymphocyte count, particularly in the mature T mu-lymphocytes, to the detriment of the B-cells which dropped in number. On the 7th day all these changes receded, however, the percent of lymphocytes with azure granules in the cytoplasm and the average number of these granules per lymphocyte cell rose. In the entire 7-day period of investigation a lowering trend was shown by the amount of serum lysozyme which dropped several times as against the initial level.