The G and P type specificity of the human rotavirus strain T-152 (G12P[9]) isolated in Thailand was serologically confirmed with G12-specific monoclonal antibodies prepared in this study by using a reference G12 strain, L26, as an immunizing antigen and a P[9]-specific monoclonal antibody, respectively. The genomic relationship of strain T-152 with representative human rotavirus strains was examined by means of Northern blot analysis. The results showed that T152 is closely related to strain AU-1 (G3P[9]). Gene 5 (NSP1 gene) of T152, which did not hybridize with those of any other strains examined, was characterized by sequence determination. The T152 NSP1 gene is 1,652 nucleotides in length, encodes 493 amino acids, and exhibits low identity to those of representative human and animal rotaviruses.