An important unresolved area of pediatric research involves the role of various viral agents in the etiology of acute gastroenteritis. Although the importance of rotaviruses is firmly established, the role of other viruses such as the astroviruses and caliciviruses has not been resolved. The goal of this project is to place these viruses in perspective with regard to their relative contribution to various forms of acute gastroenteritis in infants and young children. The availability of stool and serum specimens from several large-scale pediatric studies places us in the enviable position of being able to address these issues. Two major studies provide the focus of this project. One is a longitudinal study (1955-1969) at Junior Village, a welfare institution for homeless but otherwise normal children, and the other a cross-sectional study (1974-1991) of children hospitalized with gastroenteritis at Children's Hospital National Medical Center, Washington, DC. Our goal in the Junior Village studies has been to investigate the natural history of calicivirus and astrovirus infections in a longitudinal setting, whereas the Children's Hospital study provides materials that should allow us to determine the importance of calicivirus and astrovirus as agents of severe gastroenteritis requiring admission to the hospital. There is evidence from several studies including this one that the Norwalk viruses (now classified as caliciviruses) and astroviruses both cause infection in infants but, as yet, their importance as etiologic agents of severe gastroenteritis is not certain. This type of information must be obtained before priorities for vaccine development can be set.