One hundred and seventeen children and 41 teachers in day nurseries were screened for cytomegalovirus (CMV) viruria over a period of one year. Thirty two (27%) children and two (5%) teachers were found to be excreting virus on at least one occasion. Restriction endonuclease typing showed that virus strains isolated from the children were dissimilar, with the exception of those from sibling pairs and one unrelated pair. The virus isolate from one teacher matched those from two unrelated children, while the isolate from another teacher could not be distinguished from that from a sibling pair. The CMV serological state of the 41 teachers was not significantly different from 500 matched controls and no seroconversions occurred. It is concluded that although transmission of CMV among children and teachers may occur in day nurseries, the dissimilarity of most of the virus strains indicates that infection predominantly occurs outside. Furthermore, teachers in day nurseries showed no evidence of an increased risk of past CMV infection when compared with matched controls.