An immunogold-labelling electron-microscopic study of the frontal ganglion of two noctuids, Lacanobia oleracea and Helicoverpa armigera, has been carried out with antisera directed against three neuropeptides; allatostatins of the Y/FXFGL-NH2 type, Manduca sexta allatostatin (Mas-AS) and M. sexta allatotropin. The ganglion of both noctuids has two pairs of large peptidergic neurones with many clusters of electron-dense granules, one pair being situated anteriorly and the other posteriorly. By means of a double-labelling ("flip-flop") technique, with different sizes of gold particles, all possible paired combinations of the three different types of peptide have been visualised within granules of the anterior neurones, leading to the conclusion that the three peptides are co-packaged and co-stored in these cells. Within the posterior neurones of L. oleracea, gold labelling of granules is only linked to the Y/FXFGL-NH2 allatostatin antisera and, in contrast to the anterior cells of this species in which double gold labelling results in a sparse accumulation of gold particles for any one peptide type, single labelling gives a more intense, uniform pattern of gold particles. In contrast to L. oleracea, the gold-labelling pattern seen in the posterior neurones of H. armigera reflects the co-localisation of allatostatins of the Y/FXFGL-NH2 type with Mas-AS in this species. Allatotropin is absent in the posterior neurones of both species.