The composition of the pyrrolizidine alkaloid (PA) fraction of Senecio inaquidens was studied by capillary gc and ms. Different ionization modes were used: electron impact (ei), positive ion chemical ionization (pici) with NH,, and negative ion chemical ionization (nici) with NH, and hydroxyl ions as reagent species. Nineteen constituents were characterized and sixteen ofthem identified by these techniques. A new structure, desacetyl doronine 13) (mol wt 417), was elucidated. The application of NH, picims and OH- nicims to otonecine PA derivatives and NH, nicims to retronecine and otonecine PA derivatives is reporred and discussed for the first time.