Piriformospora indica, an endophytic fungus has been isolated in 1997 in Thar desert in India. Subsequently, a growth promoting effect of this endophytic fungus, which is similar to that of mycorrhizal fungi, could be observed in various plant species. But compared to mycorrhizal fungi, it is possible to cultivate this fungus axenically. The objective of the present work was to determine the interactions of the fungus with Arabidopsis thaliana and tomato cf. Moneymaker also in combination with the root-knot nematode Meloidogyne incognita both directly and systemicly. The colonization of roots with P.indica under long-day conditions led to significant plant growth promotion. The effect on A. thaliana demonstrated an earlier development of siliques, an increased number of siliques and an increase in yield. The existence of a systemic plant resistance against M. incognita in Arabidopsis plants colonized by the fungus could be confirmed. Further evidence was provided on the effect of fungus culture filtrate to induce growth promotion in tomato plants and to interfere with nematode infection in tomato roots.