We analysed serotype-specific antigens of human rotavirus (HRV) by the use of neutralizing monoclonal antibodies (N-MAbs). The reactivity patterns of 12 serotype-specific N-MAbs against 15 HRV strains in a neutralization test revealed great intraserotypic antigenic variation especially those belonging to serotypes 2,3 and 4. On the basis of the protein specificity of the antibodies examined, it was suggested that whereas serotype 2-specific neutralization epitopes were present on both VP3 and VP7 outer capsid proteins, serotype 1-, 3- and 4-specific neutralization epitopes were located on VP7. Serotype-specific neutralization epitopes on VP7 of the serotype 1 HRV KU strain were analysed further using mutants of the KU strain resistant to different serotype 1-specific N-MAbs. The result suggested the presence of at least five operationally overlapping neutralization epitopes on VP7 of the KU strain, which collectively constituted a single large neutralization domain.