Summary A recombinant between simian rotavirus, simian agent 11 (SA-11) and bovine rotavirus, neonatal calf diarrhoea virus (NCDV), was obtained by mixed infection of MA-104 cells with NCDV and u.v.-irradiated SA-11 virus, and isolation of a plaque formed in the presence of anti-NCDV serum. The genome of the recombinant contained dsRNA segments 4, 5 and 10 derived from SA-11 virus and segments 1, 2, 3, 6 and 11 derived from NCDV, and segments 7, 8 and 9 of undetermined origin. Polypeptides VP4, VP5, VP7a, VP7b, NCVP1 and NCVP3 were derived from SA-11 virus and polypeptides VP1, VP2, VP3, VP6, VP8, NCVP2a and NCVP2b from NCDV. Haemagglutination of the recombinant was inhibited and its infectivity neutralized by the antiserum against SA-11 virus but not by anti-NCDV serum.