We recently reported that the serotype specificity of YM, a group A porcine rotavirus, is different from those of the previously established rotavirus serotypes, 1 to 6 (A. M. Ruiz, I. V. Lopez, S. Lopez, R. T. Espejo, and C. F. Arias, J. Virol. 62:4331-4336, 1988). Here we demonstrate by cross-neutralization studies that rotavirus YM is also antigenically distinct from prototype rotavirus strains of serotypes 7 (Ty1), 8 (69M), 9 (WI61), and 10 (B223). A comparison of the serotype-determining amino acid regions of the YM surface glycoprotein, VP7, with the reported homologous sequences of rotavirus strains Gottfried, 69M, B37, F45, and WI61 further supported the serotypic individuality of the rotavirus YM VP7 protein.