The cellular localisation of two types of allatostatin in the brain and retrocerebral complex has been studied in larvae of Lacanobia oleracea (Noctuidae) using antisera against Manduca sexta allatostatin (Mas-AS) and two members of the Y/FXFGL-NH(2) allatostatin family. The axons of two groups of Mas-AS-immunoreactive neurosecretory cells in the pars lateralis form part of the nervi corporis cardiaci (NCC 1). They exit the brain as the combined NCC 1 and NCC 2 and pass through the corpora cardiaca (CC), where they divide to innervate the corpora allata (CA) and the mandibular (salivary) gland. The presence of Mas-AS immunoreactivity in the CA is consistent with the inhibitory action of this peptide on juvenile hormone (JH) biosynthesis in L. oleracea. Immunoreactivity in the mandibular gland nerve suggests an additional, as yet unidentified role for this peptide. Cells of the pars intermedialis, the main contributors to NCC 2, do not show Mas-AS immunoreactivity. The distribution of Y/FXFGL-NH(2) immunoreactivity is different from that of Mas-AS. Although there are fewer cells in the pars lateralis, immunoreactivity is observed in certain neurones of the pars intermedialis and the tritocerebrum. Axons of these latter neurones contribute to NCC 2 and NCC 3, respectively, and, combined with those from NCC 1, result in the prominent occurrence of Y/FXFGL-NH(2) immunoreactivity in the CC, particularly in the storage lobe. The CA has far less Y/FXFGL-NH(2) immunoreactivity compared with Mas-AS. In bioassays, the Y/FXFGL-NH(2) allatostatins did not inhibit JH synthesis by CA of L. oleracea.