Live cold-adapted recombinant bivalent vaccine of influenza type A was studied in a controlled field trial in 1982-1983 among nearly 30,000 children 3-15 years old. The bivalent vaccine consisted of recombinants 47/25/1 (H1N1) and 47/7/2 (H3N2) of wild-type viruses A/Brazil/11/78 (H1N1) and A/Bangkok/1/79 (H3N2) with cold-adapted donor A/Leningrad/134/47/57 (H2N2). The recombinants which received mutant nonglycoprotein genes from cold-adapted donor did not suppress each other after simultaneous inoculation of children and stimulated antibody response to both strains. The bivalent vaccine was completely attenuated for children. It caused less than 1% transient febrile reactions during five days after the first vaccination, including double seronegative individuals with low antibody titres to both vaccinal strains. The cold-adapted bivalent vaccine tested proved to be safe for children according to the analysis of morbidity studies among vaccines and a control group performed during the five days and the following six months after the first immunization. There is a similar distribution of non-influenza illnesses and a statistically significant decrease in influenza-like diseases among vaccines compared to the control group. In the four months after the immunization programme was completed, epidemics of influenza A H1N1 and H3N2 occurred. The incidence of influenza-like diseases was approximately 50% less in the vaccinated than in the control groups. This is the first evidence of safety and protective efficacy of recombinant live influenza vaccine for children 3-15 years of age.