Catecholamines (CA) are known to play an important role in the physiology of most invertebrates. Here we provide the results on catecholaminergic systems study of two annelid species: Pygospio elegans (Spionidae) and Platynereis dumerilii (Nereididae). The nervous system was studied with the histochemical method of monoamine condensa-tion with glyoxylic acid in combination with confocal laser scanning microscopy. Both animals possess developed catecholaminergic systems with similar general organization. However, in P. dumerilii considerably fewer cells were detected. In both species, CA-positive cells were found in the brain, ventral nerve cord as well as in the stomatogastric system, body wall, palps, prostomium, and regions around the chaetae. According to the cell morphology and their location in the most agile parts of the animal, we suggest CA-positive cells to be mostly proprio-or mechanoreceptors.