The pupal defensive secretion of the coccinellid beetle Epilachna borealis is composed principally of a combinatorial library of several hundred macrocyclic polyamines. This new family of natural products is characterized by extremely large-ring monocyclic polylactones, which are derived from the oligomerization of three homologous (omega-1)-(2-hydroxyethylamino)alkanoic acids. The characterization and quantification of these novel macrocyclic alkaloids as well as of related open-chain oligomers are described. Via HPLC-MS analyses of suitable derivatives, macrocycles with ring sizes from 24 to over 150 members were characterized. Whereas the three building blocks appear to be randomly incorporated into these oligomers, comparison with other ladybird beetle species suggests that the spectrum of ring sizes produced is carefully regulated.