Genes 6, 7 and 9 of human group C rotavirus 'Bristol' strain, encoding non-structural proteins (NSP) 3, 1 and 2, respectively, were cloned and sequenced. Human group C rotavirus genome segment 6 is 1350 bp and contains a single ORF of 1231 nucleotides (encoding 402 amino acids). Genome segment 7 is 1270 bp and encodes a protein of 394 amino acids and genome segment 9 is 1037 bp and encodes a 312 amino acid protein. The human group C rotavirus genes 6, 7 and 9 showed 78, 67 and 88% sequence identity, respectively, to the corresponding porcine group C rotavirus genes. The derived protein sequences were compared with those of the porcine 'Cowden' group C and mammalian group A rotavirus strains. The human group C rotavirus NSP1 protein sequence is one amino acid longer than the porcine group C equivalent. In common with group A and porcine group C rotaviruses, the human group C rotavirus NSP1 protein has a zinc finger motif. Human group C rotavirus NSP2 has two hydrophobic heptad repeat regions, a basic, RNA-binding domain and a basic, proline-rich region. Human group C rotavirus NSP3 has both single- and double-stranded RNA-binding domains and several hydrophobic heptad repeat regions, one of which forms a leucine zipper. This work completes the molecular characterization of the non-structural proteins of a human group C rotavirus. Phylogenetic analysis of all the non-structural genes of group A, B and C rotaviruses suggests that these viruses have diverged at a constant rate from a common ancestor.