Both introduced predators (e.g. domestic cats) and introduced small grazers (e.g. rabbits) are harmful to many island vertebrate species. The effects of cats on indigenous species are direct (predation), whereas the most obvious effects of rabbits are often indirect and in the longer term. Thus, in situations where both cats and rabbits are present, priority is frequently given to control of cats. However, the presence of rabbits can allow an increased predator population which can lead to extinction of the indigenous and less well adapted prey species, and increase the difficulty of predator control. Through a mathematical model, we show that control of introduced prey facilitates the control of the introduced predator population. Moreover, predator control may fail to protect the indigenous prey if control of the introduced prey is not undertaken simultaneously. Therefore, control of both introduced species is the best strategy.