Sesquiterpene pyridine alkaloids were analysed in Peritassa campestris by mass spectrometric techniques such as ESI-MSMS and GCMS. Ten alkaloids previously isolated from this plant and fully identified by other physical methods, including NMR spectroscopy and X-ray diffraction, were carefully studied by MS. It was observed that the low mass ions detected at m/z 178 and 206 in both MS technique tested were characteristic of evoninic and wilfordic acids, which are part of the macrolactone in these sesquiterpene alkaloids. The intensity of a fragment ion detected at m/z 93 in CAD, and especially in EI, spectra was found to be diagnostic in distinguishing between evoninoates and wilfordates. Running parent/daughter or GCMS experiments enabled these substances to be detected in crude fractions of P. campestris. Parent ion scans of m/z 206 were very as a first analysis of an alkaloid mixture.