The mutagenicity of a series of pyrrolizidine alkaloids, and of extracts from several Italian Senecio species containing pyrrolizidine alkaloids, including S. inaequidens, S. fuchsii and S. cacaliaster, were tested using the Salmonella typhimurium/mammalian microsome system. Retrorsine, senecivernine, seneciphylline and the Senecio extracts showed a weakly mutagenic activity.