Optimal conditions for the cultivation of the MDCK cell lines in the laboratory spinner or by using the Eagle-MEM with or without fetal serum were worked out. The cold-adapted reassortant vaccine strains of virus influenza A/H1N1, A/H3N2 and B are well replicated in the MDCK cells both in a monolayer and in the spinner by using the serum-free medium. A maximum virus titer depends on a multiplicity of infection used in a fetal medium and on the addition of trypsin. Under the optimal conditions, the titer of the studied cold-adapted reassortants, while using a serum-free medium, reaches as much as 10(9.0)-10(9.5) EID50/ml.