A study on the spatial distribution of two congeneric monogenean species Pseudodactylogyrus anguillae Yin ct Sproston, 1948 and P. bini Kikuchi, 1929 on the gills of large size European eel Anguilla anguilla (L.) were conducted. Results were analysed with regard to: single-species infection, mixed infection and general occurrence of the parasites in the ccl population. Statistical analysis revealed that the distribution of these species on the gill apparatus is fairly similar and the zones in which they occur more numerously coincide to a great extent. However, a number of differences were found. Both the possibility of simultaneous occurrence on Ihe host and similar distribution of the above species on the eel’s gills indicate the reciprocal tolerance of these parasites.