Bovine rotaviruses isolated from beef and dairy herds in Argentina were serotyped by the immunoperoxidase focus reduction assay as previously described (G. Gerna, M. Battaglia, G. Milenesi, N. Passarani, E. Percivalle, and E. Cattaneo, Infect. Immun. 43:722-729, 1984). Three strains from beef herds were related to the UK and NCDV bovine rotavirus strains defined as serotype 6 (Y. Hoshino, R. G. Wyatt, H. B. Greenberg, J. Flores, and A. Z. Kapikian, J. Infect. Dis. 149:694-702, 1984). Two other strains from dairy herds were classified as bovine viruses related to the bovine B223 strain reported by Woode and co-workers (G. N. Woode, N. E. Kelso, T. F. Simpson, S. K. Gaul, L. E. Evans, and L. Babiuk, J. Clin. Microbiol. 18:358-364, 1983) in the United States. A serotyping antibody-capture enzyme-linked immunoassay to detect serotype 6 rotavirus using a serotype 6-specific monoclonal antibody was developed and evaluated for strain characterization. Characterization of 72 group A rotavirus-positive fecal samples from beef herds and 43 fecal samples from dairy herds showed a predominance of serotype 6 rotavirus in beef herds but both serotype 6 and non-serotype 6 rotaviruses in dairy herds. Analysis of genomic double-stranded RNA by polyacrylamide gel electrophoresis showed that when outbreaks were caused by one serotype only a single electropherotype was present in all samples.