AbstractFMRFamide‐like immunoreactivity has been demonstrated in the digenean trematodeEchinostoma liei.The functions of FMRFamide‐like substances appear to be many and varied within the invertebrates, where they are involved in neurotransmission, cardiovascular regulation, muscular contraction and/or relaxation, and in co‐ordination of growth and maturation. It is clearly indicated that FMRFamide‐like substances function as neurotransmitter/neuromodulator inE. lieiby the abundance of positively stained nerve fibres and perikarya seen throughout the CNS and PNS. A single endocrine‐like cell also showing FMRFamide‐like immunoreactivity is situated within the muscular c