Sequence analysis of the gene encoding the major neutralization glycoprotein (VP7) was performed on 12 human isolates of serotype 1 of rotavirus in Japan and China. They were examined for genetic variations among serotype 1 isolates. Comparative studies of their nucleotide and deduced amino acid sequences between the 12 isolates and the Wa strain revealed an overall homology of more than 92 and 96%, respectively. Higher degrees of homologies were observed between Wa and 2 strains (K1 and K2) in Tokyo, 1979-1980, than between Wa and recent isolated strains in Tokyo and in China. In our isolates, a total of 16 amino acid residues frequently converted to another amino acid. Six amino acid residues belonging to the major neutralizing epitope regions (B, D, and E in this communication) frequently converted. From these data three subtypes (subtypes A, B, and intermediate) were suggested to be divided. Whether these differences are an important mechanism in the epidemiology of rotaviruses requires further investigation.