Influenza A viruses (H1N1 serovariant) antigenically related to swine influenza viruses were isolated in March, 1982, from two sick adolescents in a rural area of Bulgaria who had had contacts with each other and with animals. The isolates, A/PRB/120/82 and A/PRB/121/82, were found to have hemagglutinin containing antigenic regions typical of hemagglutinin of both A/New Jersey/8/76 strain and A/swine/Finister/HG/82 strain. Because of the unusual structure of hemagglutinin, it is assumed that these viruses have not been introduced into Europe from the American continent. The limited nature of the outbreak is associated with the presence in virions of A/PRB/120/82 and A/PRB/121/82 strains of NP-protein typical of animal influenza viruses.