Recently some unusual human and animal rotaviruses have been described which, although indistinguishable from standard rotaviruses by electron microscopy (EM), fail to react with antibody directed against the rotavirus group antigen. The genome of these viruses is composed of 11 double-stranded (ds) RNA segments; these RNA segments display different patterns when analysed by means of polyacrylamide gel electrophoresis (PAGE). The electrophoretic profile of the ds RNA segments of those human, antigenically different, viruses reported up to now appear to fit into two different patterns. Faecal samples from children with diarrhoea from different geographical areas of Argentina were evaluated for the presence of rotaviruses, using EM, ELISA and PAGE. During this survey a rotavirus-like agent was detected in the faeces of a child with diarrhoea from Chaco province, North-East Argentine. The pattern of the ds RNA segment of this virus on PAGE analysis appeared to be related to one of the atypical rotaviruses. This is the first description of such a virus strain in Argentina.