Many grasses live in association with asymptomatic fungi (Neotyphodium spp. endophytes), which grow in the intercellular spaces of the grass. These endophytes produce a range of alkaloids that protect the grass against grazing by mammals and insects. One of these alkaloids is an unusual pyrrolopyrazine, peramine. Peramine appears to be continuously produced by the endophyte, but does not progressively accumulate. No mechanism for the removal of peramine by its further metabolism or any other process has been reported. Our aim was to detect peramine or peramine metabolites in plant fluids to determine if peramine is mobilized, metabolized or excreted by the plant. We also wanted to determine if other fungal metabolites are mobilized by the plant, as has been proposed for the loline alkaloids. We developed a highly sensitive method for the analysis of peramine, using a linear ion trap mass spectrometer. We studied the fragmentation pathway of peramine using ESI MSn and ESI FTICRMS. Based on these results we developed a single reaction monitoring method using the fragmentation of the guanidinium moiety. Cut leaf fluid and guttation fluid of different grass endophyte associations (Lolium perenne with Neotyphodium lolii, Festuca arundinacea with Neotyphodium coenophialum, and Elymus sp. with Epichloë sp.) were analysed. Peramine was detected in the cut leaf fluid of all grass-endophyte associations, but not in the guttation fluid of all associations. In some associations we also detected lolines and ergot peptide alkaloids. This is the first report showing the mobilization of fungal alkaloids into plant fluids by the host plant in grass-endophyte associations.