In order to study the morphological and biochemical parameters of the blood of lambs affected by the causative agent of eimeria, an experimental group of animals of the Romanov breed, two months old, was formed. The lambs were spontaneously infected with the causative agent of eimeria, which was confirmed by laboratory and clinical studies. The second group of animals was free from eimeria and was kept separately. According to the results of blood tests of sick lambs, a decrease in the number of peripheral blood erythrocytes by 29.66 %, an increase in the total number of leukocytes by 47.12 % compared to the blood parameters of the control group of animals was revealed. A change in leukogram parameters was also noted: an increase in the number of eosinophils by 55.43 %, young neutrophils by 75 %. At the same time, there was a decrease in the number of rod-shaped neutrophils and an increase in the number of segmented neutrophils by 8.7 and 29.51 %, respectively. A decrease in the number of lymphocytes and monocytes by 31.68 and 12 %, respectively, was registered. Biochemical changes in the blood serum of sick lambs also underwent changes. A decrease in the content of total protein by 36.06 %, albumin by 13.09 % was established. An increase in the content of globulins and dysproteinemia was noted. Hemoglobin content was also reduced compared to blood parameters of healthy lambs by 32.25 %, as well as glucose content by 27.83 %. The activity level of ALT and AST increased by 43.43 and 33.15 %, respectively, as well as a slight decrease in GGT activity. The difference was statistically significant (Р < 0.01 and Р < 0.05). Differences in the blood parameters of sick lambs have been established and indicate a syndrome of the body's general inflammatory reaction, anemia, damage to the alimentary canal by the causative agent of eimeria and intoxication.