Rotavirus serotype G5 isolates were recently recovered from children with diarrhoea in Brazil. Like most human strains, they exhibited long electropherotypes and subgroup II and Wa-like VP4 specificity. We report the successful propagation and the molecular and antigenic characterization of one of these isolates (IAL-28). Cross-neutralization of IAL-28 and a single gene reassortant, UK x IAL-28, which contains the gene encoding the IAL-28 VP7 in the UK genomic background, with prototype G1 to G14 rotaviruses demonstrated that IAL-28 has antigenic determinants specific for both G5 and G11 serotypes. Sequence analysis of the gene encoding VP7 suggested that one or two amino acid substitutions at positions 96 and 100 on IAL-28 VP7 were possibly responsible for the additional G11 specificity. G5 rotaviruses are found in horses and predominate in piglets, whereas G11 has been identified exclusively as a swine pathogen.