AbstractNoncultivable viruses have been associated with diarrhea affecting newborn babies in obstetric hospital nurseries. Persisting infection in a special care nursery in Melbourne, Australia, permitted a study of the pattern of excretion of these viruses. Ten babies admitted to the nursery within 2 hr of birth were randomly selected for prospective study. Feces were collected daily for 14 days and were examined by electron microscopy. All ten babies excreted detectable amounts of duovirus (rotavirus, HRVL agent, IGV) for at least 1 day. Age at onset of excretion varied from 2 to 13 days. Eight of the ten babies developed diarrhea. Excretion of duovirus preceded the onset of diarrhea by 12–72 hr and persisted for at least 3 days.Seven of the ten babies also excreted detectable amounts of a 28‐nm virus‐like particle for 3–8 days. The identity of this particle is unknown. Morphologically it resembles Norwalk agent and “astrovirus.” Excretion of this 28‐nm particle coincided with symptoms of diarrhea in four babies, all of whom were also excreting duovirus.It is concluded that most newborn babies admitted to a nursery where duovirus infection is endemic will excrete this virus at least once during the first 2 weeks of life. Excretion of virus particles will either precede development of diarrhea or be asymptomatic. Selective isolation of babies with diarrhea is thus unlikely to control spread of duovirus infection within a hos