The pyrrolizidine alkaloid (PA) fraction of Senecio inaequidens DC. was studied by capillary gas chromatography-Fourier transform infrared spectroscopy. The vapour-phase IR spectra of PAs and the advantages and disadvantages of this combined technique for their structure elucidation in complex mixtures are discussed. Examples of the distinction between necine bases (retronecine and otonecine) and geometric isomers (senecionine and integerrimine) are given. © 1989.