Previous study has shown that an avian sarcoma virus-transformed quail clone, Q-B77-11, apparently contains full-size proviral DNA and releases virus particles which contain polymerase activity, but are unable to form foci. Recently, we have found that after extended tissue culture of Q-B77-11, the predominant cell type changed from one in which there was a single copy of the integrated viral DNA to one with two copies in tandem. There was approximately one copy of the large terminal redundancy between these two tandem proviruses. Polyadenylic acid-containing RNA species of twice the size of the viral genome were detected in these cells and are interpreted as transcripts of the tandem provirus.