For the development of live attenuated influenza vaccine (LAIV) against influenza virus strains with pandemic potential, method of classic genetic reassortment of donor of attenuation A/Leningrad/134/17/57 (H2N2) [Len/17] with avian apathogenic influenza viruses of different subtypes was used. Strain with genome formula 6:2, which contains HA and NA genes from avian apathogenic virus A/wild duck/Netherlands/12/00 (H7N3) [N7N3-wt] and 6 other genes--from Len/17, was studied. Reassortant strain A/17/ wild duck/Netherlands/00/84 (H7N3) [Lenl7/ H7] exhibited ts- and ca- phenotype specific for cold-adapted strains. Reassortant was identical on antigenic profile to parent avian virus H7N3-wt. Like cold-adapted donor strain Len/17, Len17/H7 was attenuated for chickens, whereas wild-type parent strain was lethal in 60% of birds after its intravenous challenge. Reassortant strain Len17/H7 was attenuated during intranasal inoculation of 6 EID50 to white mice, which was confirmed by absence of its isolation from the lungs, actively reproduced on nasal mucosa and stimulated specific systemic and local antibody response.