An increase in peroxidase activity is a common response of plants to various stresses, especially to infection by pathogens. It seemed interesting to study the effects of symbiotic fungi of fodder grasses on the peroxidase activity of their hosts. The peroxidase activity of tall fescue cv. Clarine artificially infected with Neotyphodium coenophialum or with e-endophytes from other hosts (N. lolii and LpTG-2 from Lolium perenne, Epicbloë festucae from Festuca gigantea or Koeleria cristata, Epichloë bromicola from Bromus erectus) was generally either lower or not significantly different from that of the non-infected control. Similar results were obtained with perennial ryegrass cv. Vigor artificially infected with different e-endophytes. In contrast, artificial infection of both grasses with Gliocladium-like fungi belonging to the group of p-endophytes provoked an increase in peroxidase activity. These results suggest that p-endophytes can be considered as parasites while e-endophytes, which are not able to trigger a non-specific host defence response, are really mutualistic