In Atlanta, from January to April 1975, reovirus-like agents (RLAs) were detected by a simplified electron-microscopic technique in the stools of 16 of 29 children with acute enteritis. Complement fixation tests with purified RLA antigens demonstrated antibody titer rises in seven children with RLA in their stools and in two mothers (one symptomatic) from whom acute and convalescent sera were available. Complement fixation tests performed on 207 individuals of varying ages and 60 laboratory workers indicated a high frequency of past infection with RLA, the highest frequency being in children 6 months to 4 years of age. These results corroborate the high rate of RLA detection in the stools of children with acute enteritis in other parts of the world and suggest that such infections can also occur in adults.