Ovine adenovirus OAV287 was previously isolated from sheep in Western Australia. Here we describe a portion of its genome between map units 10.3 and 31.7 which includes major ORFs for homologues of the IVa2 polypeptide and the DNA replication proteins, Terminal protein and DNA polymerase, as well as the N-terminal portion of the 52/55-kDa polypeptide. In addition, as a prelude to possible adaptation of this virus as a vector we have mapped the elements which make up the tripartite leader sequence of late mRNAs, thereby defining the probable location of the OAV major late promoter. In other human and animal adenovirus genomes, one or two VA RNA genes are encoded between the ORFs for Terminal protein and 52/55-kDa polypeptides. In OAV, these ORFs overlap, suggesting that if VA RNA genes are present, they may lie elsewhere in the OAV genome.