The accessory medulla, the circadian clock of the cockroach Leucophaea maderae, is abundant in neuropeptides. Among these neuropeptides are the FMRFamide-related peptides (FaRPs), which generally share the C-terminal RFamide. In my doctoral thesis, I aimed at gaining insights in the functional role of FaRPs in the circadian clock of the cockroach. With immunocytochemistry with antisera against various FaRPs and MALDI-TOF mass spectrometry I wanted to identify the different members of the FaRPs in the accessory medulla. With injections of two FaRPs combined with running-wheel assays I tried to clarify the role of these peptides in the circadian system. Additionally I aimed to know if FaRPs were also involved in the coupling of the bilateralsymmetric pacemakers. Prominent FMRFamide-like immunoreactivity was found in maximally four soma clusters associated with the accessory medulla and in most neuropils of the protocerebrum. By MALDI-TOF mass spectrometry, various extended FMRFamides of the cockroach L. maderae were partially identified in thoracic perisympathetic organs, structures known to accumulate extended FMRFamides in insects. By mass match, several of these peptides were also detected in the accessory medulla. Injections of FMRFamide and Pea-FMRFa-7 (DRSDNFIRF-NH2) into the vicinity of the accessory medulla caused time-dependent phase-shifts of locomotor activity rhythms at circadian times 8, 18, and 4. Thus, my data suggest a role for the different FaRPs in the control of circadian locomotor activity rhythms and in the coupling of both pacemakers in L. maderae.