Dopamine (0.08-0.25 micrograms/g of the tissue raw weight) and serotonin (0.13-0.31 micrograms/g of the tissue) were determined by spectrofluorimetry in the Opisthorchis tissue homogenate. Histochemical analysis (with glyoxylic acid) demonstrated distribution of biogenous amines in Trematode's nervous system. Fluorescence characteristic of catecholamines was found in 3 pairs of symmetrically situated cells in the anterior part of the worm and in a small number of relatively small assymmetric neurons in its posterior part. Similar fluorescence was observed in cephalic ganglia commissure, anterior and posterior nervous trunks, commissures and multiple fine fibrae. Flourescence characteristic of indolamine was seen in 5 pairs of symmetric neurons situated in the anterior part of the worm. Processes of these cells were observed from a close distance.