ABSTRACT. Presence and distribution of cholinesterases and catecholamines in the nervous system of the gill parasitic monogenean Pseudodactylogyrus bin1 from European eel Anguilla anguilla were detected by the acetylthiocholine iodide method and the glyoxylic acid method, respectively. Cerebral ganglia, opisthaptoral ganglia, longitudinal nerves and transverse commisures were positive for cholinesterase. The dorsal nerves -reacting only weakly for cholinesterase -some transverse nerves, cerebral and opisthaptoral ganglia and 2 antenor nerves were positive for catecholamines.