Ferula communis (giant fennel), a poisonous plant which causes haemorrhage, is widespread in Mediterranean rangelands and may claim the lives of up to 5 per cent of sheep grazing on infested rangelands, particularly of ewe-lambs at the first grazing season. Ingestion of giant fennel is not associated with post-ingestive pain. Two experiments were carried out with weaned ewe-lambs fed individually with a basic ration of chopped oats hay and pelleted concentrate. In experiment aversion ceased to be effective in these 2 groups between day 9 to day 16 post-dosing. In experiment 2, aversion to vetch was effective until day 19 after 1st dosing.