Baiting with medium oatmeal or soaked wheat containing 0.002, 0.001 or 0.0005% brodifacoum completely controlled infestations of warfarin-resistant rats on farms when the poisoned baits were maintained until rats ceased to feed on them. The concentration of brodifacoum did not affect the duration of these treatments which lasted from 11 to 25 days. Poison baiting with 0.002% brodifacoum for only 1,4 and 7 days achieved, respectively, only about 41, 51 and 68% control of similar farm infestations, and so emphasized the need to continue baiting for longer periods.