Over a four-month period, urine specimens for viral isolation were obtained weekly from all infants older than three weeks in two intensive care nurseries. These babies comprised 43% of the patients in the nurseries surveyed. Cytomegalovirus was cultured from 13 of 93 (14%) of these infants. Eleven of 13 infants who developed cytomegaloviruria were born prematurely, and nine of these 11 were found to be excreting CMV before they reached 40 weeks postconception. Infants excreting CMV received blood transfusions from a mean of 10.45 (+/- 1.80 SE) different donors versus 5.10 (+/- 0.55 SE) for infants without viruria (P less than 0.002) and five of 14 infants undergoing one or more exchange transfusions developed cytomegaloviruria (P less than 0.05). The possible role of other CMV reservoirs and the importance of these findings are discussed.