A study was made on the passive protection against rotavirus-induced diarrhea. Chickens were immunized with bovine rotavirus (serotype 1) and the egg yolk immunoglobulins containing a high titer anti-rotavirus neutralizing antibody (CEYI) was obtained. The CEYI was then orally administered to specific-pathogen-free cats, and the cats were infected with human rotavirus. The cats treated with the CEYI remained clinically healthy after challenge, whereas diarrhea occurred in the placebo-fed cats as control. Virus antigens were detected in feces in all the diarrheal cases in the placebo-fed cats but were only sporadically detected in the CEYI-fed cats. However, the cats were only protected against rotavirus infection by the presence in the gut at the time of infection of the antibody. These results suggested that continuous administration of the CEYI is capable of preventing children from diarrhea induced by human rotavirus infection and viral shedding.