Recently, viruses or virus-like particles have been detected by electron microscopicexamination in stools from patients with acute diarrhea; they areconsidered the causative agents of acute diarrhea (3). Among them, the humanrotavirus has been recognized as a most important pathogen of acute diarrheain infants and young children in many parts of the world. However, theseviruses associated with acute diarrhea have been identified mainly on the basisof their morphological and immunological features. Although a great deal ofeffort has been directed to adaptation of these viruses to continued propagationin cell cultures, only several animal viruses, including rotavirus strains, havebeen adapted to grow efficiently to high titer in cell culture (13). The difficultiesin propagating human enteric viruses, particularly rotavirus in conventionalcell culture systems, have hampered rapid progress in virological, serological,and epidemiological studies on viral diarrheal diseases.