The nucleic acid and deduced amino acid sequence of the fibre gene of the HNF-61 strain of porcine adenovirus serotype 5 (PAdV-5) was determined and compared to that of the HNF-70 strain of the same serotype (Nagy et al., J Gen Virol 82, 525-529, 2001) and also to adenovirus fibre genes from the genera Mastadenovirus and Atadenovirus. The putative HNF-61 and HNF-70 proteins were similar to each other, with 90% amino acid identity. Conserved amino acid sequences described for mastadenovirus fibre shafts were identified in the shaft regions of both PAdV-5 fibres, except for the so-called TLWT motif. The head regions of the PAdV-5 fibre did not resemble any of the known mastadenovirus fibre heads, but they showed characteristics of the fibre head protein sequences of viruses grouped in the proposed genus Atadenovirus (Benkö et al., Virus Taxonomy, Seventh Report of the International Committee on the Taxonomy of Viruses, Academic Press, New York, San Diego, 2000, pp. 227-238). The findings suggested recombination between viruses of different adenovirus genera.