The aim of investigations was to obtain a possibly high concentration of vaccinal strain KT of NDV propagated on 4 kinds of mammalian cell cultures: bovine foetus, kidney, calf kidney, calf node, and pig kidney cell cultures. Subjects of examination were: method of infection, dose of inoculum, temperature and time of incubation p.i., and the mode of virus harvesting. The highest virus concentration (10 7.8 EID₅₀ /0.1 ml) was obtained in the calf foetus kidney and calf kidney cells cultured in Earle's and Hanks' solutions. The optimal dose of inoculum was 10 4EID₅₀ /0.1 ml, incubation time 72 hours in 37°C. The lowest virus EID₅₀ titers, apart from the parameters used, was found in pig kidney cell culture.