AbstractA13C NMR method has been developed for obtaining simultaneously structural and quantitative information on mixtures of pyrrolizidine alkaloids fromSenecio vulgarisL. (Compositae). The samples contained seneciphylline, senecionine, retrorsine and the correspondingEgeometrical isomers, spartioidine, integerrimine and usaramine. The spin‐lattice relaxation times were measured and, after establishing the instrumental requirements for quantitative13C FT NMR, all the alkaloids of the mixture could be determined. Quantitative1H and13C FT NMR analyses were carried out, and the advantages and limitations of these methods are discusse