Poultry is one of the most intense areas of agricultural production. Biological features of chickens enable them relatively quick to get meat and egg production, which accounts for its high profitability and payback. However, the development of poultry is constrained by parasitic diseases that are widely spread and cause significant economic losses at specialized farms and private households. The issue of comprehensive study of invasive diseases is of particular importance.

One of the obstacles that hinders the development of the poultry industry is eimerias and ascariasis. The data of disease among young birds until 2 or 3 months of age manifest depression, diarrhea, often bloody, and weight loss. The death of the poultry can reach 50–70% of the number of cases, egg laying begins 1–2 months later and is much lower compared to healthy egg of uninfected poultry. The source of infestation is sick chicks and adult birds, which is often the carrier of pathogens invasion.

Among many factors that characterize the course of invasive disease, a special place is immunization. This is state of specific immunity to the action of pathogenic organisms and their metabolic products, and other foreign substances. Immunity is associated with the manifestation of complex physiological defense reactions, which provide a constant internal environment of the body.

The aim of our study was to investigate the cellular and humoral immunity in chickens infected by eimeriosis and ascaridic invasion. Changes in the biochemical composition of the blood of chickens according to experimental infestations reflect the development and pathological immune processes and points of stress conditions which allows us objectively evaluate the influence of various factors on the infested chickens. For eimeriosis invasion in serum of chickens as determined reduction of cellular and humoral immunity, and indicated by a decrease in T-and B-lymphocytes, and bactericidal activity of serum lizocyme among investigated chickens.

The main immune cells that carry out communication and interaction between all the organs of the immune system are lymphocytes. Generation of T-lymphocytes and B- lymphocytes is a physiological process that occurs in the absence of antigenic stimulation, but depends on the income of stem cells from bone marrow. B-lymphocytes, being included in the immune response after exposure to an antigen, proliferate and differentiate into plasma cells that produce immunoglobulins of three classes (A, M and G), which is the effectors of humoral immunity. One of the fundamental mechanisms of the immune system is the interaction of three types of cells – macrophages, T and B lymphocytes.

The importance of developing eimeriosis and ascaridic invasion rewuires researches of cellular immunity, which is represented by T and B lymphocytes.

Reducing the number of T-and B-lymphocytes in the blood of chickens that infested by eimerias and roundworm points to the depression of the lymphoid immune system and reduce the body's resistance against bacterial and viral infections. It should be noted that the data invasions activate pathogenic saprophyte microflora of the intestine, which also inhibits the system of cellular and humoral immunity.

Changes in cellular and humoral immunity are important objective measure of chickens body both in normal and pathological conditions. The definition of these indicators in the blood of chickens is essential for the proper functioning of the body, since its level, and the immune system in general, determine the health of chickens.

Humoral immune defense factors of poultry represent different proteins that are soluble in the blood and body fluids. They can have antimicrobial properties or capable of activating other humoral and cellular immune mechanisms against infection. It is known that humoral immunity is provided by specific macromolecules that function in domestic fowl fluids.

Under physiological conditions, the formation and the presence of circulating immune complexes in fluids is one of the manifestations of the immune response in poultry receipts antigens and an important factor in providing immunity. The results of immune complexes under these conditions, while circulating in the lymph and blood, after which they undergo elimination.

High levels of CIC in the serum of chickens indicate inhibition of immunoreactive systems of the body as a result of the accession of specific antibodies to metabolic products eimerias and roundworm that act as antigens.

Key words: parasitology, blood, chickens, T-and B-lymphocytes, serum bactericidal activity, activity lizocyme serum circulating immune complexes.