Activities of glutathione reductase (GR) (EC. 1.6.4.2) and glucose-6-phosphate dehydrogenase (G-6FDH) (EC.1.1.1.49) in erythrocytes, lactate dehydrogenase (LDH) (EC.1.1.1.27) in serum, aspartate aminotransferase (AST) (EC.2.6.1.1) and alanine aminotransferase (ALT) (EF 2.6.1.2) in the liver, brain and muscles of chickens of the local black breed during eymeriosis and treatment by 2,5% Baycox have been studied. It was found that treatment of infected birds by Baycox with dose of 2 ml/l prevents the pathological processes occurring in the body, maintainingnormalhematological parameters of blood and activity of GR. In infected birds in comparison with the control birds the activity of G-6FDH in erythrocytes decreases, and in treated chickens increases. In infected chickens activity of LDH decreases in prepatentperiod of the invasion. Baycox used for medicinal purposes, restores the activity of LDH. The change of activity in the muscles of infected birds is the same as in the liver and brain. The highest activity of AST is in the brain, liver and muscles, and ALT activity in the muscles. AST activity in liver and muscles is the same, while ALT activity in the liver is higher, than in the brain.