DNA-RNA hybridization-competition experiments were used to compare the virus-specific RNA sequences synthesized during productive infection with human adenovirus type 2 with those synthesized in virus-free adenovirus type 2 transformed cells. The "early" virus-specific RNA present at six hours after infection, prior to the onset of viral DNA synthesis, represents 8-20 percent (2 to 10 genes) of the viral genome. All viral RNA sequences synthesized early are also present "late," at 18 hours after infection. The base sequences transcribed in transformed cells are homologous to approximately 50 per cent of the sequences transcribed early after infection. Thus only 4 to 10 per cent of the viral genome, representing 1 to 5 viral genes, are transcribed in adenovirus type 2 transformed cells. The virus-specific RNA synthesized 18 hours after infection was not found in transformed cells, suggesting that either these late viral genes are not present or are not transcribed in adenovirus type 2 transformed cells.