Hepatotoxic and carcinogenic pyrrolizidine alkaloids (PAS) in phytopharmaceuticals, herbal teas, food and cattle forage are a cause of poisoning, disease and even cattle losses. On the other hand, the N-oxide of indicine has been used in trials for use as an anti-neoplastic agent [1]. Other PAS are used as markers in chemotaxonomical studies [2]. The combination of positive-ion and negative-ion chemical ionization (PICI and NICI) in gas chromatographic-mass spectrometric (GC-MS) analyses of trimethylsilyl derivatives of mono- and diester PAS offers a rapid tentative structure elucidation [3]. PICI with ammonium ions gives abundant MH + ions; cleavage of the ester bond at C-9 produces a fragment that further decomposes by elimination of the functional group at C-7, i.e. loss of trimethylsilyl alcohol (TMSOH), acetic acid, angelic acid, tiglic acid, etc. NICI with hydroxide ions cleaves ester bonds, thus generating carboxylate anions that provide a direct indication of the esterifying acids present in PAS. Identification of macrocyclic PAS is more difficult, because cleavage of one ester bond opens the macrocyclic ring. In this case the (M + OH ) - ion can often be observed [4]. Within the scope of a study of antitumour compounds in higher plants, the native Eupatorium cannabinum L. has been submitted to an extensive examination into the presence of PAS. A great number of such-like compounds could be identified using combined PICI and NICI GC-MS. Some of those have not been described before [5]. In this communication the results of a screening for PAS in roots of E. rotundifolium L. var. ovatum, a North American species, are given.