The influence of proteolytic enzymes on the increase of the sensitivity of cell cultures to Newcastle disease virus was tested in the continuous culture of goat embryo kidney cells. In this investigation the dose of trypsin and the time of incubation for the treatment of the cell culture was selected. The preliminary treatment of the monolayer culture of goat embryo kidney cells with trypsin by incubation at a temperature of 18-20 degrees C for 30 minutes made it possible to increase the sensitivity of the culture to Newcastle disease virus 10-fold.