EN
The aim of work was to select the most sensitive method of Newcastle disease virus, La Sota strain, detection in Marek’s disease vaccine and to determine its influence on replication of turkey herpesvirus (HVT), strain FC 126. It was found that the most sensitive method was the chicken embryo inoculation with contaminated vaccine. By this method the dose of 10⁰-⁵ EID₅₀ of Newcastle disease virus could he still detected. Additionally, it has been shown that La Sota strain inhibited 'replication of HVT. The dose of 10⁰-⁵ EID₅₀ of NDV reduced the number of PFU three times and replication of HVT was completely inhibited by higher doses of NDV. The inhibition of replication was probably caused by interferon produced by La Sota strain of NDV.