Sequences from genomic RNA segment 8 of the United Kingdom tissue-culture (t.c.)-adapted bovine rotavirus encoding a major viral neutralisation antigen VP7c have been expressed in Escherichia coli. Expression under the regulated control of the bacteriophage lambda pR promoter was as a C-terminal extension to E. coli beta-galactosidase (beta Gal). Following temperature induction, high levels of the fusion protein were synthesised and accumulated in induced cells, making up 5%-15% of total bacterial cell protein after 2 h of induction. Immunisation of sero-negative rabbits and mice with gel-purified fusion-protein raised antibodies, which gave specific immunofluorescence with virus-infected cells and were able to immunoprecipitate proteins of the VP7 complex from such cells. Hyperimmune sera also gave a virus-type-specific reaction in a solid-phase enzyme-linked immunoabsorbant assay and neutralised virus infectivity in standard plaque-reduction assays.