By a newly developed enzymatical characterization method for ribonucleic acid (RNA) a virus specific RNA can be detected with certainty not earlier than two hours after infection of monolayer tissue cultures of embryonic chicken cells by fowl plague virus. Almost all of this RNA is bound to the soluble antigen. After removal of the s-antigen the remaining cell-RNA, which is newly synthesized during the first three hours after infection, does not differ significantly from that of the non-infected cells.