Abstract 1. 1. The effects of synthetic biologically active peptides, including Met-enkephalin, substance P, oxytocin, Arg-vasopressin, proctolin and FMRFamide, on the following four buccal neurones were examined: d-LBAN (dorsal-left buccal anterior neurone), d-LBMN (dorsal-left buccal medial neurone), d-LBCN (dorsal-left buccal central neurone) and d-LBPN (dorsal-left buccal posterior neurone). These peptides were examined at 10 −4M. 2. 2. Oxytocin excited d-LBAN and slightly excited d-LBCN, while this inhibited d-LBMN. Arg- vasopressin excited slightly d-LBAN and d-LBCN, but this had some times no effect. FMRFamide inhibited d-LBAN, and slightly inhibited d-LBCN. 3. 3. No direct synaptic connection from the two vental cerebral giant neurones, v-LCDN and v-RCDN, to the four buccal giant neurones was found, though the two cerebral neurones innervate the cerebro-buccal connectives.