The application of NMR microscopy to the non-invasive study of internal structures in lepidopteran pupae is described and examples presented for an immature pupa of Pieris brassicae and a mature female pupa of Graphiphora augur. By using a chemical shift selective imaging procedure it was possible to determine separately the distributions of water and lipid. This technique makes it possible, in principle, to observe the relationship between the progress of metamorphosis and the utilization of lipid reserves and could thus represent a valuable new approach to the study of pupal developmental processes.