The genetic relationship between human and porcine Gp C rotaviruses and between Gp C and Gp A or B rotaviruses was examined by Northern blot hybridization. Cross-hybridization studies using radiolabeled ssRNA transcript probes demonstrated that the human and porcine Gp C rotaviruses shared a high degree of nucleotide sequence homology in most of the eleven gene segments; the greatest sequence divergence was observed in gene 7. Neither the human nor the porcine Gp C probe hybridized strongly with gene segments from Gp A reference strains or a Gp B bovine rotavirus. These data indicate that genetically, porcine and human Gp C rotaviruses are closely related, whereas they are quite distinct from Gp A or B suggesting that porcine and human Gp C rotaviruses may have evolved from a common ancestral source.