The composition of the pyrrolizidine alkaloid (PA) fraction of Senecio in-aequidens was studied by capillary gc and ms. Different ionization modes were used: electron impact (ei), positive ion chemical ionization (pici) with NH3, and negative ion chemical ionization (nici) with NH3and hydroxyl ions as reagent species. Nineteen constituents were characterized and sixteen of them identified by these techniques. A new structure, desacetyl doronine {3} (mol wt 417), was elucidated. The application of NH3picims and OH-nicims to otonecine PA derivatives and NH3nicims to retronecine and otonecine PA derivatives is reported and discussed for the first time. © 1989, American Chemical Society. All rights reserved.