It is shown that the combination of positive ion and negative ion chemical ionization (PINICI) in gas chromatography/mass spectrometry of trimethylsilyl (TMS) derivatives of pyrrolizidine alkaloids (PAS) offers a rapid tentative structure elucidation of such compounds in plant material. PICI with NH3 as the reactant gas gives abundant [MHT ions; elimination of the necic acid produces a positive ion, corresponding to the necine base, which may carry a substihaeat at C7. NICI with OH-as the reactant ion cleaves the ester bonds, which may be present at C7 and C9 of the necine base or at the p-C atom of the neck acid. This is illustrated by means of the fragmentation pattern of the PICI-and NICI-mass spectra of echinatine-(TMS),, 7-a~etyl-lycopsamine-(TMS)~, P-acetylechinatine-(TMS), supinine-(TMS), and curassavine-(TMS), (or stereoisomers). In this way, a number of 7-angelyl/tiglyl (e.g. symphytine), P-angelyl/tiglyl and @-(iso)valeryl (not reported before) derivatives of echinatine (or isomers like lycopsamine and intermedine) and of PAS with a saturated necine base, like trachelanthamine (or stereoisomers), could be shown in Symphytum taxa, Anchusa ofieinalk L. and Eupaforkm cannabhum L.