Pregnant cows were successfully hyperimmunized with all four human rotavirus serotypes, resulting in a 100-fold increase in neutralizing milk antibody titers over those of controls. Milk antibodies were isolated batchwise from 1,000 kg of pooled milk for the first 10 lactation days, yielding 10 kg of freeze-dried milk immunoglobulin concentrate consisting of 50% bovine milk immunoglobulins. Milk immunoglobulin concentrate showed neutralizing activities against all four human rotavirus serotypes that were 100 times higher than those in pooled human milk samples and 10 times higher than those in a commercial pooled immunoglobulin preparation from pooled human blood serum. In vitro neutralization tests showed that milk immunoglobulin concentrate had powerful antiviral activity, even against very high doses of infectious rotaviruses. Because the technology of the milk immunoglobulin concentrate ensures that it is innocuous and can be used for oral application, it is proposed that milk immunoglobulin concentrate be used to induce passive immunity to infantile rotavirus gastroenteritis.