Four hundred faecal samples, collected at approximately weekly intervals during the first year of life from nine babies, were examined for the presence of viruses. Only nine (2.3%) samples contained a virus detectable by electron microscopy, and on all but one occasion only one type of virus was present and that in small numbers. Thirty (7.5%) of the specimens contained an enterovirus other than poliovirus, and these represetned 10 infections in four of the children. All three types of poliovirus, probably vaccine derived, were excreted by each child, and one or more types were present in 87 (21.8%) of the samples. There was no evidence to suggest that any of the illnesses suffered by the children had been caused by faecal viruses. Infection with these viruses was uncommon in the first three months of life but more than 40% of faecal samples obtained from children between the ages of 3 months and 1 year contained a faecal virus.