Septoria tritici blotch, caused by Zymoseptoria tritici, is one of the most important diseases on wheat crops, especially in North-Western Europe, where environmental conditions are suitable for its development. Although the use of resistance inducers to control plant diseases is encouraged, their potential effectiveness on the wheat-z. tritici pathosystem remains both poorly studied and often non-significant at the field level. Ulvans are water-soluble sulphated heteropolysaccharides extracted from cell walls of Ulva spp., and known to protect plants against broad-spectrum of diseases caused by biotrophic, necrotrophic and hemibiotrophic pathogens. This study aimed at evaluating the efficacy of algal polysaccharides from ulvans on bread wheat against Z. tritici. Direct activity of ulvans on conidial germination and mycelial growth were examined in vitro at concentrations of 1 and 10 mg/ml. No effect of these polysaccharides on conidial germination was observed, but at 10 mg/ml, ulvans slightly increased mycelial growth of Z. tritici. In order to evaluate the protection efficacy of ulvans on disease expression, three-weekold wheat plants grown under greenhouse conditions were sprayed at 1 and 10 mg/ml two days before fungal inoculation ( conidia/ml). Disease evaluations 21 days later showed that ulvans can protect wheat plants against Z. tritici, and that concentration of 10 mg/ml was more effective than 1 mg/ml. As no direct effect on the fungus was observed, the level of wheat protection obtained with foliar application of ulvans should be related to the stimulation of wheat defense reactions. Further biochemical and molecular studies are being conducted to elucidate the mechanisms potentially induced by ulvans against Z. tritici in wheat.