Previous results have shown that infection of KB cells with type 5 adenovirus elicits the inhibition of host protein synthesis. In an attempt to determine whether inhibition is caused by a block in the transcription of host deoxyribonucleic acid (DNA), the rate of synthesis of host DNA-like ribonucleic acid (D-RNA) was compared with the rate of host protein synthesis at various times after infection. The rate of host D-RNA synthesis was determined by measuring the rate of incorporation of (3)H-uridine into species of ribonucleic acid which could hybridize specifically with KB cell DNA. The rate of host protein synthesis was determined by measuring the rate of incorporation of (14)C-valine into species of protein which could not be precipitated by antiserum directed against viral antigens. The results obtained suggest that the primary event producing inhibition of host protein synthesis is not the inhibition of transcription of host DNA. Synthesis of viral D-RNA in type 5 adenovirus-infected KB cells was next examined. Synthesis was first detected 8 to 10 hr after infection, and it could not be detected if viral DNA synthesis was blocked. At those times when inhibition of host protein synthesis was evident, the rate of synthesis of viral D-RNA appeared to exceed that of KB cell D-RNA.