The fearsome fox, an introduced pest, has been and continues to be a disaster for our small native mammals, as well as a nuisance for farmers. The CSIRO Division of Wildlife and Ecology has set up a program to devise an efficient method of control. The biologists' strategy centres on rendering the pests sterile by using their own immune systems to attack their gametes (eggs and sperm). In effect, the animals will be inoculated against themselves. But rather than injecting the animals, the researchers hope to use a virus, to which genes for proteins found on fox egg and sperm will be added, to perform the inoculation.