[RNA-polymerase activity of pathogenic and nonpathogenic influenza A virus variants]. 
The transcriptase activity of original mouse-apathogenic strains of human (A/USSR/05/81) and animal (A/walrus/Massachusetts/1/80) influenza viruses and their pathogenic variants was studied.  Also RNA-polymerase was studied in two types of antigenic recombinants produced by hybridization of the parental strains one of which (A/PR8/34) was pathogenic for mice.  The nonpathogenic viruses under study were shown to have a low transcriptase activity, while pathogenic variants of these strains had a higher RNA-polymerase activity (1 1/2-3 times higher than in the original virus).  All the recombinants tested, irrespective of their pathogenicity, had approximately similar transcriptase activity, 1 1/2-2 times higher than the enzymatic activity of the parental nonpathogenic virus.