Bovine adenovirus type 3 (BAV3) is a DNA virus that causes respiratory and gastrointestinal disorders in cattle. We have sequenced the extreme left end of BAV3 genome (0-11.7 map units). Partial analysis of the nucleotide sequence revealed 19 potential open reading frames (ORFs) that could encode for polypeptides of 50 or more amino acids. Four of these ORFs show homology to known adenovirus polypeptides. The four BAV3 ORFs are located in approximately the same area as the Ad5 E1a, E1b, and pIX ORFs. ORF 1 has the potential to code for a 208 amino acid long polypeptide that is 75.5% homologous to the E1a conserved region III of Ad5. ORFs 2 and 3 encode 157 and 420 amino acid long polypeptide, respectively. The 157 amino acid polypeptides exhibits 69.3% homology to the Ad5 small T antigen, and the 420 amino acid polypeptide exhibits 73% homology to the large T antigen of Ad5. ORF4 has the potential to code for a 125 amino acid long polypeptide that has 73% homology to the hexon-associated pIX of Ad7.