The c.d. curves of seventeen pyrrolizidine alkaloids have been measured, together with curves for the component parts of these alkaloids, viz pyrrolizidine bases and necic acids. The curves are discussed in relation to the nature and relative positions of the chromophores, first for the component acids and bases and then for the macrocylic alkaloids. Some c.d. curves have been measured at low temperatures as well as at room temperature; some 0.r.d. curves have also been measured.