Genetic cross was performed in human conjunctival cell cultures between two strains of influenza A virus, Ao/NWS and A2/Hong Kong, both of which plaque with high efficiency on the above cells and which differ from each other in some genetic markers. Clones of progeny virus from mixed infection were isolated in the absence of selective procedures and individually tested for the following marker characteristics; the serotype of the hemagglutinin and the neuraminidase, plaque size, plaque forming capability on FL cells, and requirement of DEAE-dextran for plaque formation. Characterization of 42 clones showed the recombination frequency in two factor cross between the above markers ranged from 18 to 43%. There was no indication of linkage between the markers employed. From the absence of recombination within the serotype of the hemagglutinin or that of the neuraminidase, it was suggested that recombination occurs mainly by exchange of cistrons. Three clones were suspected to be initiated by partially heterozygous virus particles.