Group C rotaviruses have been identified recently from fecal samples of children with diarrhea in the United States. Using reverse transcriptasepolymerase chain reaction and sequence analysis, we sequenced gene 8s encoding VP7 from two U.S. strains (RI-1 and RI-2), and eight other strains isolated from patients on four continents, and compared these with the sequences of four published strains. The gene 8s of the 14 strains were remarkably conserved in size and in predicted primary and secondary structures. When the sequences of the human VP7s were compared with that of the prototype porcine Cowden strain, six regions were found variable in both deduced primary and predicted secondary structures, four of which were predicted to be hydrophilic and might determine serotype specificity. Gene 8 of the human S-1 strain was further characterized by expression in recombinant baculoviruses. The expressed product was immunogenic but failed to elicit neutralizing antibodies. Our sequence analysis indicates that all the human strains characterized to date belong to a single G genotype, which may constitute a single G serotype, pending further antigenic analysis. Whether the human strains and the Cowden strain are the same serotype remains to be determined.