The effects of poly(I) poly(C12U) (Ampligen) on infections with enteric viruses (rotavirus, poliovirus and Coxsackie B3 virus) were studied in vitro. Ampligen exhibited antiviral activity against rotavirus, especially when treatment was performed prior to inoculation of the virus. It was partially effective against Coxsackie B3 virus, but not against poliovirus. It is suggested that the observed effects may be due to the production of interferon induced by Ampligen.