The genomic region between map units 69 and 78 of a type 3 porcine adenovirus (PAV3) was sequenced and analysed. An open reading frame (ORF) of 2514 nucleotides encoding a polypeptide of 838 amino acids and approximately 94.1 kDa was found. The size and location of the ORF suggested it was the PAV3 homologue of the 100K gene and this was confirmed by nucleotide sequence comparison with the 100K of human adenovirus type 2. Amino acid sequence alignment of the predicted polypeptide with the sequences of the 100K proteins of four human adenoviruses and type 10 fowl adenovirus revealed sequence identities of between 31% and 52%. Although amino acid conservation was present throughout the entire sequences compared, lower identity was noted in both the amino- and carboxy-termini.