The genomic organization of the simian virus 40 (SV40)-adenovirus (Ad)7 hybrid virus, PARA(cT), was examined. A deletion of approximately 5529 bp of Ad7 DNA extends from 78.8 map units to 94.0 map units and is replaced by an SV40 DNA insert of 3809 bp. The left-hand end of the insertion begins at SV40 nucleotide 5168, 5 bp upstream of the ATG initiation codon for T-ag synthesis. The sequence extends counterclockwise through the T-ag encoding sequences and into SV40 late region DNA. Most of the late region DNA has been removed in a deletion between nucleotides 2464 and 301. One of the 72-bp repeats has also been deleted. The right-hand end of the SV40 DNA insert is at nucleotide 4366. Thus, a portion of the SV40 DNA early region is repeated at both ends of the insert (nucleotides 5168-4366).