AbstractThe efficiency of crossed immunoelectrophoresis (CIE) for the determination of taxonomic relationships between populations of two different selected animal groups has been investigated employing eight populations of the family Tisbidae and eleven populations of the family Enchy‐traeidae grown under laboratory conditions. Antisera were raised in rabbits against extracts from twoTisbeand threeEnchytraeuspopulations. The antisera were used in CIE in homologous and heterologous combination with antigens of each population of the two groups. Numbers of heterologous immunoprecipitates were counted and divided by the numbers of the corresponding homologous combination. A decrease in the resulting values (matching coefficients) represents a decrease in the degree of relationship between the populations.The relationship patterns resulting from the CIE analysis showed within the genusTisbetwo pairs of closely related populations:T. holothuriae/T. battagliaiandT. gracilis/T. cucumariae. T. bulbisetosaandT. furcataclearly were different species but the position of these species within the genusTisbecould not exactly be determined.Within the genusEnchytraeustwo groups of very closely related populations could be distinguished: (1.) E, F, and G; (2.) C and A. These two groups form a larger group of six closely related populations including also population D. The speciesE. albidus, E. bigeminusandE. frag‐mentosustogether form another group which is more distant to these six populations. The populations J and B are even more remote from t