Possible mechanisms involved in the suppression of the take all fungus (Gaeumannomyces graminis var, tritici) by a sterile red fungus were examined. Studies on the effects of foliar application of thiamine to plants showed a reduction in take-all suppression by the sterile red fungus thereby indicating that competition for this particular vitamin, required by both fungi, could be one of the mechanisms of antagonism. Treatment with the exudate produced by the sterile red fungus on solid substrates resulted in lysis of the hyphae of the take-all fungus. Exudate produced on sterilised wheat seeds was more inhibitory to the take-all fungus than that produced on ryegrass seeds. Fungal inhibition increased as the duration of exposure to the exudate increased. The primary effects of hyphal interactions between the sterile red fungus and the take-all fungus were evident as coiling and contact lysis. It is possible that a combination of mechanisms including the above may be involved in suppression of the take-all fungus by the sterile red fungus.