Of 73 rotavirus-positive fecal specimens tested, 39 yielded a human rotavirus that could be cultivated serially in MA104 or primary African green monkey kidney cells or both; 18 were serotyped. Four distinct serotypes were identified by plaque reduction or tube neutralization assay or both, and three of these serotypes were the same as those established previously by plaque reduction, using human rotaviruses cultivated by genetic reassortment with a cultivable bovine rotavirus. Ten human rotavirus strains received from Japan were found to be similar, if not identical, to our candidate prototype strains representing these four human rotavirus serotypes.