Necrotrophic mycoparasitic and strong competitive ability ofFusarium lini Bolley, a root pathogen of linseed (Linum usitatissimum L.), was observed against some potential fungal root colonizers. The antagonistic nature ofF. lini was studied on nutrient agar and root surface in the presence of background antagonism. The results are discussed in the light of general factors involved in antagonism during the colonization of substrate.