Wild populations of house mice (Mus domesticus) regularly undergo population eruptions in the cereal growing regions of S.E. Australia, causing significant damage to crops. Rodenticides are costly and are of limited usefulness, and the need for a biological control agent is widely recognized. The options for the use of an infectious agent to control mouse populations are considered. The three main types are: infectious agents which establish lethal infection; those which directly interfere with fertility; and recombinant virus vectors encoding fertility-associated proteins such as zona pellucida or sperm antigens in order to induce immunocontraceptive responses in infected mice. Ectromelia, a murine pox virus, has the potential for reducing mouse populations by lethal infection but it is not present in wild mice in Australia. The disadvantages of using ectromelia are that it would pose a significant threat to colonies of laboratory mice, there appears to be substantial innate resistance in Australian wild mice and it may not be entirely mouse-specific, thus placing native rodents at risk. A number of factors influencing the selection of a virus as a vector for immunocontraception are discussed. The mouse-specific murine cytomegalovirus (MCMV) fits most of these criteria. Infection with MCMV is already widespread in Australia with 80-90% of Mus domesticus tested being seropositive. It is a large DNA virus which establishes persistent, non-lethal infection, it is a suitable vector for the insertion of foreign genes and has a number of properties, including the capacity for superinfection, that should assist the recombinant virus to persist in wild mouse populations and induce an immunocontraceptive effect.