Newcastle disease is one of the most significant diseases in the poultry industry. By induction of specific immunoprotection of poultry, an aim is to induce a sufficient amount of antibodies to the Newcastle disease virus and thus adequate protection to prevent the outbreak of epizootics. Due to the different routes of administration of the vaccine and the different effect of the vaccine on the immune response, it is important to monitor antibody titers of vaccinated poultry in order to obtain a better view of the acquired protection. The purpose of this thesis is to analyze the results of ELISA titers of specific antibodies to Newcastle disease in several flocks of layer hens longitudinally on two farms to acquire the dynamics of gained titers. Immunoprophylaxis of Newcastle disease in layers on monitored farms consists of repeated administration of a live attenuated vaccine, first administered by spraying chickens in a hatchery and then twice by drinking water, most commonly using the La Sota strain. After that, and immediately before the transfer to the production facilities, a polyvalent inactivated vaccine is used which is applied i.m. or s.c. A commercial ND ELISA kit (Biochek, The Netherlands) according to the manufacturer's instructions was used to detect the titer of specific antibodies to Newcastle disease virus. In our study, 36% (7) of the total tested flocks (19) have a satisfactory antibody titer according to manufacturer's reference values, 41% and 27% on farm 1 and farm 2, respectively. Out of a total of 168 hens, 65 have an adequate protective titer according to reference values, or 38 %. Also 26% of flocks (5 of 19) have adequate %CV and 31% (6 of 19) have adequate VI. Higher variability and lower titers should be expected in younger flocks, below 20 weeks af age, while in older flock we detected lower titers and higher variability, what could be result of improper vaccination program as well as lower number of samples per flock. According to that 32 it is important to control the vaccination protocol as well as blood sampling and sample storing, and to take proper number of samples.