Ewes were vaccinated two to three weeks prior to mating with a formalin-treated preparation of lamb rotavirus. The colostrum and milk produced by vaccinated ewes after the subsequent pregnancy were shown to contain significantly higher titres of antibody to the virus than did mammary secretions from non-vaccinates. The virus neutralising antibody activity was associated with IgG in both colostrum and milk. However, IgG concentrations in the mammary secretions of vaccinates and non-vaccinates did not differ. It is suggested that vaccination of the dam may be of value in protecting the suckled neonatal lamb against rotavirus infection.